Peptide Glossary

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5-Amino-1MQ

Not a peptide. A small-molecule NNMT (nicotinamide N-methyltransferase) inhibitor investigated for body composition and metabolic effects via NAD⁺ preservation. Frequently sold alongside peptides on research-chemical sites; no human approval.

503A Pharmacy

A pharmacy that compounds medicines under section 503A of the Federal Food, Drug, and Cosmetic Act, for individual patients on a practitioner's prescription. It may compound from a bulk drug substance only if the substance has a USP monograph, is a component of an approved drug, or is on FDA's 503A bulks list.

503B Outsourcing Facility

A compounding facility registered with FDA under section 503B. It can make medicines without individual prescriptions but must follow current good manufacturing practice and is inspected by FDA.

A

Abarelix

The first injectable GnRH antagonist for prostate cancer — a synthetic decapeptide that achieved castration without testosterone flare, later supplanted by degarelix and oral alternatives. Encyclopedia entry

ACE-031

A myostatin decoy receptor that raised lean mass after one dose in healthy women; its Duchenne trial was stopped in 2013 over nosebleeds and dilated vessels. Encyclopedia entry

Acetate Salt

A common counter-ion in synthetic peptides. A peptide supplied as an acetate salt includes acetate in its stated mass, so the amount of peptide itself is somewhat lower than the weight on the label.

Acetyl Hexapeptide-30

Inyline — Lipotec's post-synaptic cosmetic peptide. Unlike Argireline-family pre-synaptic SNAP-25 mimetics or Vialox-style nAChR antagonists, Acetyl Hexapeptide-30 is claimed to block the agrin-MuSK interaction that maintains post-synaptic AChR clustering; was formerly INCI Acetyl Hexapeptide-25. Encyclopedia entry

Acetyl Hexapeptide-37

The Lipotec "Diffuporine" cosmetic peptide — identified by luciferase-reporter combinatorial screening as an AQP3 inducer; increases epidermal water transport and barrier proteins at cosmetic concentrations; entirely topical, no systemic development. Encyclopedia entry

Acetyl Octapeptide-3

The 'Super Argireline' — an extended SNAP-25 fragment peptide that reduces expression wrinkles without injections. Encyclopedia entry

Acetyl Tetrapeptide-2

Uplevity — a Lipotec firming tetrapeptide proposed to support dermal mechanotransduction by organising elastin, fibulin-5, and LOXL-family enzymes. Follow-on "skin architect" peptide marketed as alternative to pre-synaptic/post-synaptic muscle peptides; manufacturer-only efficacy data. Encyclopedia entry

Acetyl Tetrapeptide-5

Eyeseryl — the anti-puffiness eye peptide. A β-alanine-containing acetyl-tetrapeptide claimed to reduce capillary permeability and inhibit glycation-driven cross-linking; low absolute concentrations (0.01 % active) but convincing before/after in manufacturer studies. Encyclopedia entry

Achondroplasia

The most common form of short-limbed dwarfism, caused by a gain-of-function mutation in FGFR3. Vosoritide (Voxzogo) is the first FDA-approved treatment — a C-type natriuretic peptide analog that counteracts the overactive FGFR3 signaling.

Acylation

Attachment of a fatty acid chain to a peptide to extend half-life via albumin binding. Semaglutide's C18 diacid at Lys26 and liraglutide's C16 mono-acid at Lys26 are examples of acylation engineering.

Adamax

An enhanced Semax derivative with an adamantane modification borrowed from P21, studied in limited Russian research for BDNF upregulation and cognitive enhancement. Encyclopedia entry

Adipotide

A preclinical concept that killed white adipose tissue by inducing vasculature apoptosis in obese rhesus monkeys — dramatic weight loss, but also nephrotoxicity that stopped it from advancing to humans. Encyclopedia entry

Adlyxin

US brand name for lixisenatide, a short-acting GLP-1 receptor agonist. Marketed by Sanofi for type 2 diabetes. Discontinued in the US in 2023 but still available in other markets (as Lyxumia in EU).

Adnectin

An engineered protein scaffold based on the 10th fibronectin type III domain, designed as an antibody-alternative for target binding. Taldefgrobep-alfa is a myostatin-targeting adnectin.

Adrenomedullin

A 52-amino-acid vasodilator hormone discovered in 1993, infused in small trials for pulmonary hypertension, ulcerative colitis and Crohn's disease; the bowel-disease trials missed their primary end points. Not approved. Encyclopedia entry

Afamelanotide

An FDA-approved selective MC1R agonist marketed as Scenesse — the first-in-class treatment for erythropoietic protoporphyria (EPP), delivered as a subdermal implant. Encyclopedia entry

Agonist

A molecule that binds to a receptor and activates it, producing a biological response. Semaglutide is a GLP-1 receptor agonist — it binds to and activates GLP-1 receptors, mimicking the natural ligand.

AHK-Cu

A tripeptide copper complex studied primarily for hair follicle stimulation and anagen induction in cosmetic applications. Encyclopedia entry

Aib

α-Aminoisobutyric acid. A non-standard amino acid resistant to DPP-4 and neprilysin degradation. Used at position 8 of semaglutide and tirzepatide to block proteolytic cleavage and extend half-life.

Albiglutide

A once-weekly GLP-1 receptor agonist made by fusing two copies of GLP-1 to human albumin. FDA-approved in 2014 as Tanzeum and now discontinued, it cut major cardiovascular events by 22% against placebo in Harmony Outcomes. Encyclopedia entry

Allosteric

Binding at a site on a receptor distinct from the primary (orthosteric) binding site. Allosteric modulators can enhance or blunt the response to the natural ligand without directly activating the receptor themselves.

Alpha-MSH

The endogenous anti-inflammatory melanocortin — the 13-amino-acid POMC fragment that PT-141, melanotan, setmelanotide, and the entire melanocortin drug class are built on. Encyclopedia entry

Alprostadil

A synthetic prostaglandin E1 vasodilator FDA-approved for intracavernosal use in erectile dysfunction and for maintaining ductus arteriosus patency in neonatal congenital heart disease. Encyclopedia entry

Amino Acid

The building blocks of peptides and proteins. Twenty standard amino acids are used to build human peptides, each with a unique side chain. The sequence determines structure and function.

AMPK

AMP-activated protein kinase, a cellular energy sensor activated when ATP is low. In animal studies, MOTS-c acts in part through AMPK.

Amycretin

Novo Nordisk's investigational single-molecule GLP-1 and amylin receptor agonist, tested as a daily tablet and a weekly injection: in a phase 1b/2a trial the 60 mg weekly dose gave a mean weight change of -24.3% at 36 weeks against -1.1% on placebo. Not approved anywhere. Encyclopedia entry

Amylin

A 37-amino-acid peptide hormone co-secreted with insulin by pancreatic beta cells. Slows gastric emptying and promotes satiety. Pramlintide, cagrilintide, petrelintide, and AzD6234 are amylin analogs.

Anamorelin

An oral ghrelin agonist that adds lean mass in cancer cachexia but never beat placebo on strength: approved in Japan, not in the US. Encyclopedia entry

ANDA

Abbreviated New Drug Application. The FDA pathway for generic drugs, which relies on showing sameness and bioequivalence to an approved reference drug instead of repeating its efficacy trials. Generic liraglutide exists; compounded drugs are not generics.

Angiogenesis

The formation of new blood vessels from existing ones. Animal and cell studies of BPC-157 report pro-angiogenic effects linked to VEGF signalling; they have not been confirmed in people.

Angiotensin II

The body's blood-pressure hormone as an ICU drug: Giapreza raised pressure in seven of ten patients in shock; survival did not significantly change. Encyclopedia entry

ANP

The heart's salt-excreting hormone: sold in Japan as carperitide since 1995, while US kidney trials of anaritide found no benefit. Encyclopedia entry

Antagonist

A molecule that binds a receptor but blocks its activation, preventing the natural ligand from producing its effect. Atosiban, ganirelix, and cetrorelix are peptide antagonists.

Anti-Drug Antibodies (ADAs)

Antibodies the body makes against a therapeutic peptide or protein. They can reduce a drug's effect or cause hypersensitivity reactions, and drug labels report how often they appear. Development of taspoglutide, a GLP-1 analogue, was halted after hypersensitivity reactions.

Antimicrobial Peptide (AMP)

A peptide of the innate immune system that kills or inhibits microbes through membrane disruption or intracellular targets. LL-37, defensins, KR-12, FK-13, pexiganan, and omiganan are examples.

Antimicrobial Resistance (AMR)

The ability of microorganisms to withstand antimicrobial treatments. Antimicrobial peptides (AMPs) are being investigated as alternatives to conventional antibiotics because their membrane-disrupting mechanisms make resistance development less likely.

AOD-9604

A 16-amino-acid piece of growth hormone that trimmed fat in obese rodents; in company trials it was well tolerated, but its largest obesity trial found no significant weight loss and development stopped in 2007. Encyclopedia entry

Apelin

The natural ligand of the APJ receptor, discovered in 1998: in short human infusion studies it widened arteries through nitric oxide and, in kidney disease, lowered blood pressure and raised kidney blood flow. A research peptide; no apelin drug is approved. Encyclopedia entry

Apitegromab

⚠ Monoclonal antibody, not a peptide. Scholar Rock's antibody against the proforms of myostatin, FDA-approved on September 11, 2026 as Isembyld for spinal muscular atrophy in patients 2 and older already on an SMN2-targeted treatment. Encyclopedia entry

Apraglutide

Ironwood's weekly GLP-2 analog for short-bowel syndrome — STARS Phase 3 positive (2024), NDA submitted to FDA 2025; potentially the first once-weekly SBS therapy and a meaningful improvement over teduglutide's daily dosing. Encyclopedia entry

ARA-290

An 11-amino-acid EPO-derived peptide studied for neuropathic pain and tissue protection, without the red-cell-stimulating effects of full erythropoietin. Encyclopedia entry

Argireline

A cosmetic-industry hexapeptide marketed as "topical Botox" — reduces muscle contraction signaling at the neuromuscular junction; modest but documented effects on expression-line depth. Encyclopedia entry

Atosiban

Ferring's Tractocile — an oxytocin-receptor antagonist used in Europe and elsewhere as a tocolytic for short-term suppression of preterm labor between 24 and 33 weeks' gestation. Approved by the EMA in 2000; the FDA declined to approve atosiban in 1998 citing a higher fetal/infant death rate in the <26-week subgroup of the pivotal trial. Encyclopedia entry

AUC

Area Under the Curve. The integrated concentration-time exposure of a drug — a measure of total drug exposure over a dosing interval. Used to compare bioequivalence and dose-response.

AZD6234

AstraZeneca's long-acting amylin analog — Phase 2 in obesity (2024) — part of AZ's entry into the GLP-1-adjacent obesity space alongside ECC5004; analogous in mechanism to cagrilintide. Encyclopedia entry

B

Bacitracin

The topical first-aid antibiotic — one of the most widely used over-the-counter peptide antibiotics, found in virtually every household first-aid kit. Encyclopedia entry

Bacteriostatic Water (BAC Water)

Sterile water containing 0.9% benzyl alcohol as preservative. The standard diluent for reconstituting peptides. Unlike sterile water, inhibits bacterial growth for up to 28 days after the seal is first pierced.

BAM15

Not a peptide. A mitochondrial protonophore (uncoupler) studied preclinically for obesity and metabolic disease. Early research stage; often stocked by peptide-adjacent vendors.

Barth Syndrome

A rare X-linked genetic disorder of mitochondrial cardiolipin remodeling that causes cardiomyopathy and muscle weakness. Elamipretide (Forzinity), the clinical form of the research peptide SS-31, is approved to treat it.

BDNF

Brain-Derived Neurotrophic Factor. A protein supporting neuron survival, growth, and synaptic plasticity. Semax, Selank, Dihexa, and exercise all upregulate BDNF.

Beinaglutide

Recombinant human GLP-1 with the natural 30-amino-acid GLP-1(7-36) sequence, injected three times daily; used for type 2 diabetes in China, and in a 16-week phase 3 trial it cut weight by 6.0% against 2.4% on placebo. Not FDA- or EMA-approved. Encyclopedia entry

Beta-Endorphin

The body's most potent endogenous painkiller — the 31-amino-acid opioid peptide behind the 'runner's high' and natural pain modulation. Encyclopedia entry

Biased Agonism

When a receptor agonist preferentially activates one signaling pathway over another from the same receptor (e.g., G-protein vs β-arrestin). Ecnoglutide is described as a cAMP-biased GLP-1 agonist.

Bimagrumab

The activin receptor antibody that adds muscle and removes fat: failed in a muscle disease, now paired with semaglutide for obesity. Encyclopedia entry

Bioactive Food Peptides

The hidden pharmacology of food — bioactive peptide fragments released during digestion of milk, meat, fish, and plant proteins, including casomorphins, lactokinins, and ACE-inhibitory peptides. Encyclopedia entry

Bioavailability

The fraction of a dose that reaches the circulation. Semaglutide injected under the skin is about 89% bioavailable; swallowed as a tablet it is about 1% to 2% (Wegovy label). Enlicitide tablets are about 1% (Lipfendra label).

Biologic

A therapy derived from or produced in living systems — recombinant proteins, monoclonal antibodies, cell therapies. Insulin, somatropin, and dulaglutide are biologics; synthetic peptides like BPC-157 technically are not.

Bioregulator (Khavinson Peptide)

Short synthetic peptides (2–4 amino acids) developed by Vladimir Khavinson's Russian group, each targeting a specific tissue (pineal, thymus, cardiac, cerebral cortex, etc.). Examples: Epithalon, Cartalax, Pinealon, Thymogen.

Biotinoyl Tripeptide-1

A biotin-peptide hybrid for hair loss — combining GHK's tissue repair signaling with biotin to strengthen follicles and reduce thinning. Encyclopedia entry

Bivalirudin

Angiomax — the workhorse direct thrombin inhibitor for percutaneous coronary intervention. FDA-approved December 2000 (The Medicines Company, now Sandoz); the first synthetic peptide DTI to achieve broad PCI adoption. REPLACE-2, ACUITY, and HORIZONS-AMI trials established the anticoagulant profile; subsequent MATRIX trial outcomes shifted practice in some populations back toward heparin. Encyclopedia entry

BLA

Biologics License Application. The FDA pathway for biological products, including proteins, which FDA defines as more than 40 amino acids (growth hormone and insulin, for example), antibodies and vaccines. Most peptide drugs are approved through NDAs instead.

Black Box Warning

The FDA's strongest label warning, printed in a box. Ozempic, Wegovy, Mounjaro and Zepbound carry one for thyroid C-cell tumors seen in rodents; their labels say it is unknown whether the drugs cause these tumors in humans.

BMI

Body Mass Index. Weight (kg) / height² (m²). Defines eligibility for several peptide therapies: Wegovy requires BMI ≥30 (or ≥27 with comorbidity). A crude metric — does not distinguish fat from lean mass.

BNP

The hormone a stretched heart releases: a standard blood test for heart failure since 2000, and the discontinued drug nesiritide. Encyclopedia entry

Body Composition

The proportion of lean mass vs. fat mass in the body. Measured via DEXA, BodPod, or multi-frequency bioimpedance. Peptide protocols often target composition change (GH secretagogues aim for lean-mass gain + fat loss) rather than weight alone.

Botulinum Toxin

A bacterial toxin that cleaves SNAP-25 to silence nerve endings: approved for migraine, bladder, spasticity and more, under a boxed warning. Encyclopedia entry

BPC

Body Protection Compound, a name for peptides derived from a protein in gastric juice. BPC-157, a 15-amino-acid fragment, is the one sold and studied, mostly in animals.

BPC-157

A synthetic pentadecapeptide from gastric protein, widely studied in animal models for tendon, ligament, and gastrointestinal healing. Encyclopedia entry

Bradykinin

The peptide behind wheals, leaky vessels and asthma narrowing; never a treatment, but its B2 blocker icatibant treats angioedema attacks. Encyclopedia entry

Bradykinin System

A signaling pathway involving the peptide bradykinin, which promotes vasodilation, pain, and inflammation. Dysregulation causes hereditary angioedema. Icatibant (Firazyr) is an FDA-approved bradykinin B2 receptor antagonist used to treat acute attacks.

BRN2 (POU3F2) Research Peptide

A research-only peptide derived from the POU3F2 (BRN2) neural transcription factor; mechanistic and phenotypic evidence is limited almost entirely to in vitro and lineage-specification studies. No human therapeutic development, no clinical trials, no established dosing, and no commercial availability through regulated channels. Encyclopedia entry

Bronchogen

A Khavinson tetrapeptide from bronchial tissue — proposed to support respiratory epithelium function in chronic obstructive airway disease; evidence is preliminary and Russian-language. Encyclopedia entry

Buserelin

A GnRH agonist widely used in Canada, the UK, Germany, and other markets (Suprecur, Suprefact) for prostate cancer, endometriosis, and IVF downregulation — but never FDA-approved in the United States. Encyclopedia entry

C

C-Terminus

The end of a peptide chain with a free carboxyl (–COOH) group. Peptide sequences are conventionally written N-terminus → C-terminus (left to right).

Cagrilintide

Novo Nordisk's weekly, lipidated amylin analogue: up to 10.8% weight loss alone in a 26-week phase 2 trial, and with semaglutide as CagriSema 20.4% over 68 weeks in REDEFINE 1. Investigational; not approved anywhere. Encyclopedia entry

CagriSema

Novo Nordisk's next-generation obesity injection — NDA filed December 2025, FDA review expected 2026. If approved, it would be the first GLP-1 + amylin fixed-dose combination and a direct competitive response to tirzepatide. Encyclopedia entry

Calcitonin

The hormone that switches off bone-dissolving cells: one 1,255-woman fracture trial, and a later option now that stronger drugs exist. Encyclopedia entry

cAMP

Cyclic adenosine monophosphate. A second messenger generated when Gs-coupled receptors (including GLP-1R, GHRH-R, PTH-R) are activated. Cyclic AMP is the canonical signal for most peptide-hormone-driven actions.

Capromorelin

⚠ Veterinary use only — not approved for humans. Elanco's oral ghrelin agonist (Entyce for dogs 2016, Elura for cats 2020) — FDA-approved only for veterinary appetite stimulation. Included for completeness because it is a genuine approved ghrelin receptor agonist with significant online search volume. Encyclopedia entry

Carbetocin

Ferring's Pabal / Duratocin — a long-acting oxytocin analogue given once after birth to prevent postpartum haemorrhage. Heat-stable carbetocin matched oxytocin in WHO's 29,645-woman CHAMPION trial, and WHO's 2025 guideline recommends carbetocin for all births. Not FDA-approved. Encyclopedia entry

Cardarine (GW501516)

Not a peptide. A PPARδ agonist small molecule studied for endurance and metabolic effects; development was abandoned after rodent carcinogenicity findings. WADA-prohibited; still sold by research-chemical vendors despite the safety signal.

Cardiogen

A Khavinson-group tetrapeptide from heart-tissue extract — proposed to support cardiomyocyte function and cardiac tissue aging; evidence base is Russian-language and largely pre-clinical. Encyclopedia entry

Carnosine

β-alanyl-L-histidine, the dipeptide concentrated in muscle and brain that buffers acid and resists glycation; as a supplement, small trials are mixed, and a 299-person trial found no general effect on physical performance. Encyclopedia entry

Carperitide

⚠ Approved in Japan only (1995). Recombinant human ANP infused for acute heart failure and used in more than half of Japanese admissions in one study, but its outcome evidence conflicts: a propensity-matched analysis linked it to higher in-hospital mortality, and its randomised LASCAR-AHF trial stopped early without showing benefit. Encyclopedia entry

Cartalax

A Khavinson tripeptide from cartilage tissue extract — proposed to support chondrocyte function and joint tissue homeostasis in aging and osteoarthritis models; mostly pre-clinical Russian-language evidence. Encyclopedia entry

Catecholamine

Neurotransmitter/hormone family including dopamine, norepinephrine, and epinephrine. Several neuropeptides (Semax, Selank) modulate catecholaminergic systems.

Cathelicidin

hCAP18, the precursor the body cuts to release LL-37: switched on by vitamin D, measured in blood and urine, never given as a treatment. Encyclopedia entry

Cecropin

The insect immune system's first-line antibiotic — among the earliest AMPs discovered, proving innate immunity uses peptide weapons across the animal kingdom. Encyclopedia entry

Cerebrolysin

A pig-brain peptide mixture approved in about 50 countries for stroke and dementia; Cochrane found no survival benefit after stroke and more non-fatal serious adverse events. Encyclopedia entry

Cerluten

A Khavinson lung-derived short peptide bioregulator sold in Russia as a cytomedine supplement for respiratory aging. Like the rest of the Khavinson short-peptide family, supporting evidence is almost exclusively Russian-language and of low methodological rigor by Western standards; no independent replication, no FDA or EMA status, and no controlled clinical data. Encyclopedia entry

Certificate of Analysis (COA)

A document from an independent third-party lab confirming a peptide product's identity, purity, and concentration. Reputable vendors provide batch-specific COAs using HPLC and mass spectrometry.

Cetrorelix

Merck Serono's Cetrotide — a GnRH antagonist used during IVF controlled ovarian stimulation to block premature LH surges. Unlike GnRH agonists, produces immediate gonadotropin suppression without a flare, shortening IVF cycles. Encyclopedia entry

cGMP

Cyclic guanosine monophosphate. Second messenger produced when natriuretic peptide receptors (NPR-A) or guanylate cyclase-C receptors (activated by linaclotide, plecanatide) are stimulated.

CGRP

The vasodilating neuropeptide behind migraine attacks: infused, it triggers them, and drugs that block it now prevent them. Encyclopedia entry

Cholecystokinin

The gut hormone that empties the gallbladder after meals; its octapeptide, sincalide (Kinevac), is FDA-approved for diagnostic tests. Encyclopedia entry

Chonluten

A Khavinson tripeptide studied for bronchial epithelium regeneration and anti-inflammatory effects in the respiratory tract — evidence base is Russian-language and preliminary. Encyclopedia entry

CJC-1295

A long-acting GHRH analog engineered with a DAC linker that binds serum albumin, extending half-life from minutes to approximately 8 days. Encyclopedia entry

Clinical Trial (Phase 1/2/3)

Staged testing in people. FDA describes phase 1 as 20 to 100 volunteers testing safety and dosage, phase 2 as up to several hundred people with the condition testing efficacy and side effects, and phase 3 as 300 to 3,000 people testing efficacy and monitoring adverse reactions. Phase 4 studies follow approval.

Cmax

Maximum concentration. The peak blood level of a compound after administration. Cmax is reached at Tmax and then declines per the compound's half-life.

CNP

The third natriuretic peptide — a vascular and skeletal growth factor whose analog vosoritide (Voxzogo) is FDA-approved for achondroplasia, and the endogenous cartilage growth signal. Encyclopedia entry

Colistin

Polymyxin B's sibling — a cyclic lipopeptide antibiotic revived from the 1950s as the ultimate weapon against pan-drug-resistant gram-negative bacteria, despite significant nephrotoxicity. Encyclopedia entry

Collagen Peptides

Hydrolysed collagen taken by mouth, a mixture of short peptides rather than one molecule. Randomised trials at 2.5 to 15 g a day report better skin elasticity and hydration, higher bone mineral density in postmenopausal women, less activity-related knee pain. A dietary supplement, not an approved medicine. Encyclopedia entry

Colostrinin

A colostrum-derived polypeptide complex — studied in clinical trials for Alzheimer's disease, with immunomodulatory activity that shifts cytokine profiles from pro- to anti-inflammatory. Encyclopedia entry

Compounded Medication

A custom-prepared medication made by a licensed pharmacist under a prescription. Compounding is allowed under 503A/503B rules; peptide compounding eligibility depends on FDA bulk-substance lists and shortage status.

Compounding Pharmacy

A pharmacy that prepares medicines under section 503A (for individual prescriptions) or as a 503B outsourcing facility. Compounding is lawful only within those sections' conditions, and many peptides sold online meet none of them; the regulatory tracker shows each peptide's status.

Conotoxin

Disulfide-rich peptides found in cone snail venom, often highly selective for ion channels and receptors. Ziconotide (Prialt) is the most prominent example — an FDA-approved conotoxin for severe chronic pain.

Contraindication

A condition in which a medicine should not be used, as stated on its label. GLP-1 medicines are contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2. Research peptides have no labels, so no contraindications have been established for them, which is not the same as being safe for everyone.

Copper Peptide

A peptide bound to a copper(II) ion. GHK-Cu, found naturally in human plasma, is the prototype; it is used in cosmetics, and the evidence for other uses is mostly cell and animal work.

Corifollitropin alfa

Elonva — recombinant FSH fused to the C-terminal peptide of hCG (about 65-hour half-life), given as one injection to replace the first week of daily FSH in IVF cycles. Authorised in the EU since January 2010; never approved in the US. Encyclopedia entry

Cortagen

A Khavinson-group tetrapeptide isolated from cortex tissue — used in Russian neurology practice for post-stroke cognitive deficit; evidence is almost entirely Russian-language with minimal Western replication. Encyclopedia entry

Cortexin

A polypeptide extract of calf or pig brain cortex, injected in Russia after stroke and for cognitive problems; its trials are Russian and none is placebo-controlled. Encyclopedia entry

Corticorelin

Ferring Pharmaceuticals' synthetic ovine CRH (Acthrel) — FDA-approved diagnostic peptide used to distinguish pituitary Cushing disease from ectopic ACTH secretion via inferior petrosal sinus sampling or peripheral ACTH/cortisol response testing. Encyclopedia entry

Cosmetic Peptide

A peptide formulated for topical skincare rather than systemic effect. Includes matrikines (Matrixyl), neuropeptide mimetics (Argireline), copper peptides (GHK-Cu), and enzyme modulators (SNAP-8, Syn-Ake).

Cotadutide

A GLP-1 and glucagon dual agonist that reached phase 2b in diabetes, kidney and liver disease before AstraZeneca stopped it in 2023. Encyclopedia entry

CRP (C-Reactive Protein)

A liver-produced acute-phase inflammation marker. High-sensitivity CRP (hs-CRP) is tracked for low-grade systemic inflammation. GLP-1 agonists, BPC-157, and TB-500 have shown CRP-lowering effects in some studies.

Cyclic Peptide

A peptide whose chain forms a ring rather than a linear sequence, often conferring enhanced stability and receptor binding. Octreotide, lanreotide, and melanotan analogs are cyclic.

Cycling

Alternating on- and off-dosing periods, intended to prevent receptor desensitization, hormonal suppression, or tachyphylaxis. Common in GH-secretagogue protocols (8–12 weeks on, 4 weeks off).

Cytokine

Cell-signaling protein regulating immune responses and inflammation. Many peptides modulate cytokine release — e.g., thymosin alpha-1 shifts the cytokine profile toward Th1.

Cytoprotective

Protecting cells from damage. BPC-157 is described as cytoprotective because it helps shield cells in the GI tract and other tissues from various forms of injury.

D

D-Amino Acid

The mirror-image stereoisomer of a natural L-amino acid. D-amino acids resist proteolysis, extending half-life. FOXO4-DRI is named for its D-retro-inverso design; many GnRH analogs use D-amino acid substitutions.

Dalton (Da)

A unit of molecular weight. Most therapeutic peptides range from 500 to 5,000 Da. BPC-157 is ~1,419 Da; semaglutide is ~4,114 Da; insulin is ~5,808 Da.

Danuglipron

⚠ Not a peptide — small molecule. Pfizer's discontinued oral GLP-1 program — halted April 14, 2025 after a single case of potential drug-induced liver injury in a once-daily dose-optimization study, ending Pfizer's second oral GLP-1 failure in as many years. Included in this peptide encyclopedia because the audience frequently searches for it alongside peptide GLP-1 agonists. Encyclopedia entry

Daptomycin

A last-resort lipopeptide antibiotic — the first-in-class cyclic peptide that kills MRSA and VRE by depolarizing bacterial membranes, without resistance through traditional mechanisms. Encyclopedia entry

Davunetide

NAPVSIPQ, the minimum active fragment of ADNP — an 8-amino-acid neuroprotective peptide studied in Phase 2 (cognition in mild cognitive impairment, schizophrenia) and Phase 3 (progressive supranuclear palsy). The Phase 3 PSP trial failed in 2012; development continues in schizophrenia (Coronis / ATL-104) and ADNP syndrome research. Encyclopedia entry

DEA Schedule

The Controlled Substances Act's five schedules, I to V. Most peptides are not controlled substances. Human growth hormone is not scheduled either, but federal law separately restricts distributing it for unapproved uses.

Decapeptide

A peptide containing exactly 10 amino acids. GnRH (gonadotropin-releasing hormone) and its analog leuprolide are decapeptides.

Decorinyl

The INCI name for the active peptide in Decorinyl® — a tetrapeptide (KDI-Cit) whose charge pattern (+/−/0/+) reproduces decorin's collagen-binding motif. Decorinyl is the trade name of this molecule; both names lead to this entry. Encyclopedia entry

Defensin

A family of small cationic antimicrobial peptides produced by neutrophils and epithelia. Alpha-defensins (HNP-1, HNP-2, HNP-3, HD5, HD6) and beta-defensins (hBD-1, hBD-2, hBD-3) defend against bacteria, fungi, and some viruses.

Degarelix

An approved GnRH antagonist (Firmagon) for advanced prostate cancer: castrate testosterone by day 3 in 96% of men, no flare, but frequent injection-site reactions and an unsettled heart-safety question. Encyclopedia entry

Delta Opioid Receptor

One of three classical opioid receptors, activated primarily by enkephalins. Modulates pain, mood, and neuroprotection. Research peptides targeting delta receptors aim to achieve analgesia with fewer respiratory and addictive side effects than mu-targeting drugs.

Denaturation

Unfolding or structural disruption of a peptide or protein, causing loss of biological activity. Shaking vials, excessive heat, extreme pH, or freeze-thaw cycles can denature peptides.

Dermcidin

The antibiotic peptide in human sweat, found at lower levels in eczema and acne, and never given to anyone as a treatment. Encyclopedia entry

Dermorphin

⚠ Potent mu-opioid agonist — ~30–40× more potent than morphine; has been misused as a horse-racing doping agent and carries serious overdose/dependence risk. Included for reference and harm-reduction only. Not a therapeutic or "longevity" peptide. Encyclopedia entry

Desensitization

Also called downregulation. A reduction in receptor responsiveness after prolonged or excessive agonist exposure. Why some peptides are cycled.

Desmopressin

DDAVP — the classic V2-selective vasopressin analog. FDA-approved February 1978 for central diabetes insipidus; decades of label expansion added primary nocturnal enuresis, nocturia (Noctiva / Nocdurna), and hemostatic use in mild hemophilia A and type 1 von Willebrand disease. WHO Essential Medicines List. Encyclopedia entry

DEXA

Dual-Energy X-ray Absorptiometry. The gold-standard scan for body composition, bone mineral density, and visceral fat. A common tracking tool in serious peptide protocols (GH secretagogues, GLP-1 agonists, MOTS-c).

Dihexa

A modified dipeptide built from angiotensin IV to reach the brain by mouth: rodent memory studies only, no human data, and the paper tying it to HGF/c-Met is retracted. Encyclopedia entry

Diluent

A liquid used to dissolve lyophilized peptide. Bacteriostatic water is the standard choice; sterile water, normal saline, or acetic acid solutions are used in specific cases.

Dipeptide

A peptide consisting of exactly two amino acids joined by one peptide bond. Carnosine (β-alanine + histidine) and Thymogen (Glu-Trp) are naturally and synthetically derived dipeptides.

Disulfide Bond

A covalent bond between two cysteine residues, stabilizing peptide tertiary structure. Oxytocin, vasopressin, somatostatin, and insulin all rely on disulfide bonds for proper folding.

Downregulation

A reduction in the number or sensitivity of receptors after prolonged agonist exposure. Why some peptide protocols cycle — to prevent the receptor 'turning off' that blunts effect.

DPP-4

Dipeptidyl Peptidase-4. An enzyme degrading native GLP-1 and GIP in ~2 minutes. Most GLP-1 analogs incorporate DPP-4-resistant substitutions (e.g., Aib at position 8) to extend half-life.

DSHEA

Dietary Supplement Health and Education Act of 1994, the law that set the US framework for dietary supplements. Peptides sold as supplements generally lack the required status: an ingredient introduced after 1994 needs a new dietary ingredient notification, and one first approved or studied as a drug is excluded from supplements.

DSIP

A nine-amino-acid peptide isolated from rabbit brain blood in 1977 and named for delta-wave sleep, whose sleep effects in human trials were weak and inconsistent. Encyclopedia entry

Dual Agonist

A single molecule activating two distinct receptors. Tirzepatide (GLP-1/GIP), cagrisema/pemvidutide (GLP-1/glucagon), and cotadutide (GLP-1/glucagon) are examples.

Dulaglutide

A once-weekly GLP-1 receptor agonist built on an antibody fragment (Trulicity), approved since 2014 for type 2 diabetes in adults and children 10 and older. In REWIND it cut major cardiovascular events by 12%; semaglutide beat it head to head. Encyclopedia entry

Dynorphin

The brain's 'anti-reward' opioid — a kappa-receptor agonist that produces dysphoria rather than euphoria, critical to understanding addiction, stress, and depression. Encyclopedia entry

E

ECC5004

An oral small-molecule GLP-1 receptor agonist, not a peptide, developed by Eccogene and then AstraZeneca; a phase 3 trial registered in 2026 names it elecoglipron. Encyclopedia entry

Ecnoglutide

Sciwind's once-weekly, cAMP-biased GLP-1 analogue (half-life 124-138 h): approved in China for type 2 diabetes (January 2026) and chronic weight management (March 2026) after phase 3 trials, including 13.2% weight loss at 40 weeks. Not FDA- or EMA-approved. Encyclopedia entry

Efpeglenatide

A weekly-to-monthly exendin-4-based GLP-1 agonist with positive Phase 3 cardiovascular outcomes (AMPLITUDE-O, 2021) — Sanofi returned the license to Hanmi in 2020; Hanmi re-partnered with Innovent in 2020 for China development and with Kailera in 2024 for global development. Encyclopedia entry

Eftansomatropin alfa

Genexine and Handok's long-acting growth hormone, somatropin fused to a hybrid Fc; in development, with a Chinese licence application filed and no approval found as of October 2026. Encyclopedia entry

Elagolix

The first oral GnRH antagonist — a non-peptide small molecule that suppresses estrogen production without injection, FDA-approved for endometriosis pain. Encyclopedia entry

Elsiglutide

Zealand Pharma's early GLP-2 analogue (ZP1846), tested in phase 2 for chemotherapy-induced diarrhoea; no later trials are known. Encyclopedia entry

EMA

European Medicines Agency. The EU's drug regulatory body, roughly analogous to FDA. Issues marketing authorizations valid across EU/EEA. Many GLP-1 agonists are EMA-approved in parallel with FDA.

Endogenous

Produced naturally within the body. Endogenous peptides include insulin, oxytocin, GLP-1, and endorphins. Contrast with exogenous (administered externally).

Endogenous Peptide

A peptide naturally produced within the body, as opposed to synthetic or exogenous peptides. Examples include beta-endorphin, neuropeptide Y, and cholecystokinin. Understanding endogenous peptides is essential for grasping how synthetic analogs and mimetics work.

Endoluten

The Khavinson pineal bioregulator preparation, positioned as a "precursor/complementary" product to epithalon (the synthetic AEDG tetrapeptide). Marketed in Russia for neuroendocrine and circadian support in aging. Evidence base is Russian-language Khavinson-group studies with minimal independent replication. Encyclopedia entry

Endothelin-1

One of the body's most potent vessel constrictors: a drug target for pulmonary hypertension, given to people only in experiments. Encyclopedia entry

Enkephalin

The body's short-acting local painkillers — five-amino-acid opioid peptides that modulate pain, mood, and gut motility at the synaptic level. Encyclopedia entry

Epithalon

A synthetic pineal tetrapeptide from Vladimir Khavinson's St. Petersburg group, with telomerase and telomere-length data from cell cultures and little human evidence. Encyclopedia entry

Eptifibatide

A cyclic heptapeptide that blocks platelet glycoprotein IIb/IIIa, modelled on barbourin from the venom of the southeastern pigmy rattlesnake. FDA-approved as Integrilin on May 18, 1998 for acute coronary syndromes and coronary intervention; now sold as generics. Encyclopedia entry

Erythropoietin (EPO)

A glycoprotein hormone that drives red blood cell production; recombinant forms are FDA-approved standards of care for anemia of chronic kidney disease and chemotherapy-induced anemia, and have a notorious history of misuse in endurance sport. Encyclopedia entry

Exenatide

The first GLP-1 receptor agonist (Byetta, 2005), a synthetic copy of a Gila monster venom peptide: safe for the heart in EXSCEL without proving benefit, outperformed by weekly semaglutide head to head, and negative in a phase 3 Parkinson's trial. Encyclopedia entry

Exogenous

Introduced from outside the body. Therapeutic peptides are exogenous — synthetically produced and administered to supplement or mimic endogenous signaling.

F

FAK-Paxillin Pathway

Focal adhesion kinase signalling, involved in cell migration and adhesion during wound healing. A cell study of BPC-157 reported activation of this pathway in tendon fibroblasts.

Fc Fusion

A peptide or protein fused to the Fc region of an immunoglobulin, extending half-life through FcRn-mediated recycling. Dulaglutide (GLP-1-Fc) and eftansomatropin-alfa (GH-Fc) are Fc-fusion therapeutics.

FDA

US Food and Drug Administration. Regulates drug, biologic, device, and food marketing in the United States. Approval status (approved / IND / research-only / unapproved) is the single most important regulatory dimension for peptides.

FDA Approved

The peptide has gone through a complete NDA or BLA and is marketed as a prescription medication for specific approved indications. Ozempic, Wegovy, Mounjaro, Zepbound, Saxenda, Victoza, and Bremelanotide (Vyleesi) are FDA-approved.

Felypressin

The vasopressin analogue added to prilocaine dental anaesthetics instead of adrenaline, approved widely abroad and never in the US. Encyclopedia entry

FGF21

Fibroblast Growth Factor 21. A metabolic hormone released from liver under stress; improves insulin sensitivity and lipid metabolism. Some pipeline peptides (e.g., GMA106) combine GLP-1 with FGF21 activity.

FGL Peptide

A 15-amino-acid synthetic peptide derived from the second fibronectin-type-III module of NCAM, designed to mimic NCAM's interaction with FGFR1 and reproduce downstream neurogenic signaling. Preclinical cognition and neuroprotection data only; no human clinical trials; research-only. Encyclopedia entry

FK-13

The 13-residue FKRIVQRIKDFLR central fragment of LL-37 — the smallest LL-37 fragment that retains broad-spectrum antimicrobial activity while losing much of the parent peptide's cytotoxicity toward mammalian cells. Research-only; no clinical development program. Encyclopedia entry

Follistatin-315

The full-length follistatin found in human blood: it keeps an acidic tail that weakens its grip on cell surfaces, so it circulates while the shorter FS288 stays tissue-bound. Encyclopedia entry

Follistatin-344

The myostatin blocker tested only as gene therapy in six men, sold online in vials that often do not contain it. Encyclopedia entry

Follitropin alfa

Recombinant human FSH (Gonal-f), approved in the US on September 29, 1997, the same day as follitropin beta: daily injections that grow ovarian follicles for ovulation induction and IVF and, with hCG, restart sperm production in men with hypogonadotropic hypogonadism. Encyclopedia entry

Follitropin beta

Organon/Merck's Follistim AQ (Puregon internationally) — a recombinant human FSH produced independently of follitropin alfa but clinically equivalent; FDA-approved 1997 for ovulation induction and IVF controlled ovarian stimulation. Encyclopedia entry

Follitropin delta

Ferring's Rekovelle — a recombinant human FSH produced in a human cell line (PER.C6), dosed via a personalized algorithm based on serum AMH and body weight. Approved in the EU, UK, Canada, Australia, Japan, and China, but received an FDA Complete Response Letter in February 2026 over manufacturing issues; not currently approved in the United States. Encyclopedia entry

FOXO4-DRI

A senolytic peptide that clears senescent cells in mice and cultured cells, and has never been given to a person. Encyclopedia entry

FSH

Follicle-Stimulating Hormone. Pituitary gonadotropin driving follicle development in ovaries and spermatogenesis in testes. Follitropin-alfa, -beta, -delta, urofollitropin, and corifollitropin-alfa are therapeutic analogs.

G

Galanin

A neuropeptide with uniquely broad functions — modulating seizures, pain, mood, and neurogenesis across three receptor subtypes. Encyclopedia entry

Ganirelix

The GnRH antagonist that keeps an IVF cycle from ovulating early, and cut the protocol from weeks of injections to days. Encyclopedia entry

Garetosmab

An anti-activin A antibody approved in 2026 for fibrodysplasia ossificans progressiva, after a phase 2 that missed its primary endpoint. Encyclopedia entry

Gauge (G)

Needle thickness measurement — higher number = thinner needle. Peptide subcutaneous injections typically use 29G, 30G, or 31G insulin syringes. Thinner needles hurt less but may clog more easily with viscous solutions.

GDF11

Not a peptide: the TGF-β protein reported in 2013-2014 to rejuvenate old mouse hearts and muscle, then disputed over faulty assays. Never tested in people. Encyclopedia entry

GDF15

⚠ Not a peptide — a 12 kDa TGF-β superfamily protein. Rises with age and with mitochondrial stress; a potent anorexic/cachexia signal via its brainstem GFRAL/RET receptor. Active clinical development in two directions: agonism for obesity (NGM120, LY3463251) and antagonism for cachexia (ponsegromab, Pfizer Phase 3 PROACC-1 in cancer cachexia). Encyclopedia entry

Generic (Peptide)

A non-branded equivalent of an approved peptide. Generic versions of most newer peptides (semaglutide, tirzepatide) don't yet exist due to active patents. Compounded versions are legally distinct from generics.

GH (Growth Hormone)

A 191-amino-acid protein secreted by the anterior pituitary. Drives IGF-1 production, protein synthesis, lipolysis, and counter-regulation of insulin. Recombinant forms (somatropin, somapacitan) are used therapeutically.

GH Secretagogue

A compound that stimulates growth hormone release from the pituitary. Examples include CJC-1295, Ipamorelin, Sermorelin, Tesamorelin, and the oral non-peptide MK-677.

GHK-Cu

A copper-binding tripeptide found in human plasma and sold widely in skin care; the evidence is mostly cell and animal work, with few trials in people. Encyclopedia entry

Ghrelin

The 'hunger hormone' produced mainly in the stomach. Ipamorelin, GHRP-2, GHRP-6, Hexarelin, MK-677, Anamorelin, Capromorelin, and Relamorelin act at the ghrelin (GHS-R) receptor.

GHRH

Growth Hormone Releasing Hormone. A hypothalamic hormone stimulating pituitary GH release. CJC-1295, Sermorelin, Tesamorelin, and Mod-GRF-1-29 are synthetic GHRH analogs.

GHRP-2

The second-generation GHRP, approved only in Japan (as pralmorelin) for a one-dose growth hormone test: a reliable growth hormone releaser that also raises ACTH, cortisol and appetite, and was never approved as a treatment. Encyclopedia entry

GHRP-6

The original growth hormone-releasing hexapeptide: a strong, fast releaser in 1990s human tests that also raises ACTH and cortisol. Encyclopedia entry

GIP

Glucose-dependent Insulinotropic Polypeptide. An incretin hormone enhancing insulin secretion. Tirzepatide is a GLP-1/GIP dual agonist; retatrutide is a GLP-1/GIP/glucagon triple agonist.

Glatiramer Acetate

A synthetic peptide polymer for multiple sclerosis — one of the first disease-modifying therapies for MS, mimicking myelin basic protein to shift the immune response from attack to tolerance. Encyclopedia entry

Glepaglutide

A once- or twice-weekly GLP-2 analogue for short bowel syndrome whose phase 3 met its endpoint on the twice-weekly dose. Encyclopedia entry

GLP-1

Glucagon-Like Peptide-1. An incretin hormone stimulating insulin, suppressing glucagon, slowing gastric emptying, and reducing appetite. Semaglutide, liraglutide, exenatide, dulaglutide, tirzepatide, and orforglipron all target GLP-1.

GLP-2

Glucagon-Like Peptide-2. An intestinotrophic hormone promoting mucosal growth. Teduglutide, apraglutide, and glepaglutide are GLP-2 analogs used primarily in short-bowel syndrome.

Glucagon

A 29-amino-acid pancreatic hormone raising blood glucose through hepatic glycogenolysis and gluconeogenesis. Dual/triple agonists (retatrutide, mazdutide, survodutide, pemvidutide) target glucagon to enhance energy expenditure alongside GLP-1.

Glutathione

The tripeptide antioxidant every cell makes. Oral doses raised body stores in a six-month trial; IV drips sold for skin lightening have little controlled evidence. Encyclopedia entry

GMA106

Gmax Biopharm's anti-GIPR antibody fused to a GLP-1 peptide, in development for obesity; one completed Phase 1 trial, no published results. Encyclopedia entry

GMP / cGMP

(Current) Good Manufacturing Practice. FDA quality standards covering facility, equipment, personnel, testing, and documentation for pharmaceutical production. 503B facilities must follow cGMP; 503A pharmacies must meet USP compounding standards.

GnRH

Gonadotropin-Releasing Hormone. A hypothalamic decapeptide driving pituitary LH and FSH release. Gonadorelin is the natural form; leuprolide, goserelin, triptorelin, histrelin, nafarelin, and buserelin are agonists; cetrorelix, ganirelix, and degarelix are antagonists.

Gonadorelin

Synthetic GnRH, the hypothalamus's pulse signal for LH and FSH: pumped every 60 to 120 minutes it restored ovulation and sperm production in trials, but as an occasional injection beside testosterone it has never been studied. Encyclopedia entry

Gonadotropin

A hormone targeting the gonads — LH, FSH, and hCG. Drives sex-steroid production and gametogenesis. Menotropin, lutropin-alfa, urofollitropin, and hCG are gonadotropin preparations.

Goserelin

Zoladex, a GnRH agonist set in a biodegradable implant placed under the skin every 28 days (3.6 mg) or 12 weeks (10.8 mg, men only). US-approved since 1989 and labelled for prostate cancer and, at 3.6 mg only, for advanced breast cancer before menopause, endometriosis and endometrial thinning. Encyclopedia entry

Gramicidin

One of the first antibiotics, isolated in 1939: too toxic to swallow or inject, still used in combination eye and ear drops. Encyclopedia entry

Gvoke

Brand name for a ready-to-use auto-injector glucagon formulation (Xeris Pharmaceuticals) for severe hypoglycemia rescue.

H

Half-Life

The time it takes for a drug's concentration in the blood to fall by half. Semaglutide's is about a week (Ozempic label), which allows weekly dosing; native GLP-1 is broken down within minutes.

HbA1c

Glycated hemoglobin. A lab marker reflecting average blood glucose over the prior 2–3 months. The primary efficacy endpoint for GLP-1 agonists and insulins in type 2 diabetes trials.

hBD-1

The constitutive epithelial β-defensin — first isolated from haemodialysate urine by Bensch, Schröder and colleagues (FEBS Letters 1995). Constitutively expressed (unlike hBD-2 and hBD-3, which are inducible), salt-sensitive in standard assays, and a major component of urogenital and airway surface antimicrobial defense. Encyclopedia entry

hBD-2

The inducible β-defensin — cloned by Harder, Bartels, Christophers and Schröder (Nature 1997) from the lesional scales of psoriasis patients, with the paper framing psoriatic skin as a paradoxical "almost-never-infected" phenotype driven by massive β-defensin induction. Induced by TLR / NF-κB signalling in response to bacterial lipopolysaccharide and pro-inflammatory cytokines (IL-1, TNF-α). Encyclopedia entry

hBD-3

The broad-spectrum β-defensin — active against Gram-positive, Gram-negative and fungal targets, and largely salt-insensitive (unlike hBD-1). Isolated independently in 2001 by Harder et al. and by García et al. from psoriatic skin and tonsil respectively. The β-defensin most studied for clinical translation because of its salt tolerance. Encyclopedia entry

HCG

A prescription fertility hormone that acts like LH: the IVF trigger and a treatment for male hypogonadism, used off-label beside testosterone on the strength of two small studies, and shown not to work for weight loss. Encyclopedia entry

HD5

The Paneth cell α-defensin — the dominant antimicrobial peptide of the human small intestine, stored at millimolar concentrations in Paneth cell secretory granules and released into the crypt lumen upon cholinergic or bacterial stimulus. Reduced HD5 expression is a recognised feature of ileal Crohn disease. Encyclopedia entry

HD6

The Paneth cell defensin that traps gut bacteria in self-assembled nanonets instead of killing them; lower in Crohn's disease. A research subject, never a drug. Encyclopedia entry

Health Canada

Canada's federal health regulator, which approves and oversees drugs. Most major GLP-1 medicines are approved there.

Hereditary Angioedema (HAE)

A rare genetic condition causing severe episodes of tissue swelling due to uncontrolled bradykinin signaling. Treated with peptide-based drugs including icatibant (a bradykinin antagonist) and lanadelumab (an anti-kallikrein antibody).

Hexapeptide

A peptide containing exactly 6 amino acids. GHRP-6, hexarelin, and argireline (acetyl hexapeptide-3) are hexapeptides.

Hexarelin

A synthetic GH-releasing hexapeptide that outperformed GHRH in small 1990s human studies, also raised cortisol and prolactin, and lost part of its effect with months of use. Never approved. Encyclopedia entry

Histatin

The histidine-rich salivary peptides that kill Candida and close wounds, trialled twice in dentistry and never marketed. Encyclopedia entry

Histrelin

A GnRH agonist implant that suppresses puberty for twelve months at a time; the prostate-cancer version has been discontinued. Encyclopedia entry

HM15136

A weekly glucagon analogue in early trials for congenital hyperinsulinism, where raising blood sugar is the point. Encyclopedia entry

HM15275

Hanmi's triple-agonist GLP-1/GIP/glucagon candidate, mechanistically analogous to retatrutide — Phase 2 in obesity with a monthly-dosing ambition enabled by Hanmi's LAPSCOVERY platform. Encyclopedia entry

HNP-1

The prototype human α-defensin — isolated from neutrophil granules by Ganz, Selsted and Lehrer in 1985; the dominant antimicrobial peptide in human neutrophils and a workhorse molecule of innate immunity. Research peptide only: no defensin has ever been developed as an approved drug. Encyclopedia entry

HOMA-IR

Homeostatic Model Assessment of Insulin Resistance, an index calculated from fasting glucose and fasting insulin. It tracks insulin sensitivity and can improve with weight loss and with GLP-1 medicines.

HPLC

High-performance liquid chromatography, the standard method for measuring a peptide's purity. It separates a sample's components and reports the main peak's share; it does not confirm identity, which needs mass spectrometry. No official purity grade applies to research-use products.

HRS-9531

Hengrui's once-weekly GLP-1/GIP dual agonist in Phase 3 in China for obesity, with Kailera Therapeutics holding global ex-China rights since 2024; the structurally closest Chinese competitor to tirzepatide. Encyclopedia entry

Humanin

A 24-amino-acid mitochondrial-derived peptide with neuroprotective and cytoprotective activity. First discovered in 2001, humanin established the concept that mitochondrial DNA encodes bioactive peptides.

Humatrope

Eli Lilly's brand of somatropin (recombinant human growth hormone). One of the oldest marketed rhGH products, available in multi-dose pen and vial formats.

Hyaluronic Acid

A sugar chain, not a peptide: FDA-approved as fillers and joint injections, brand by brand, with thinner evidence as a supplement. Encyclopedia entry

Hypoglycemia

Low blood glucose. GLP-1 agonists alone rarely cause hypoglycemia (glucose-dependent insulin secretion), but combined with sulfonylureas or insulin the risk rises substantially.

I

Ibutamoren (MK-677)

An oral, non-peptide ghrelin-receptor agonist: it raised growth hormone and IGF-1 for months in trials and added lean mass in older adults, but failed in Alzheimer's and hip-fracture recovery, raised blood sugar and was never approved. Encyclopedia entry

Icatibant

The bradykinin blocker for angioedema — a synthetic decapeptide B2 receptor antagonist that stops acute swelling attacks within 30 minutes. Encyclopedia entry

IGF-1

Insulin-like Growth Factor 1. A hormone produced mainly in the liver in response to GH. IGF-1 blood levels are the primary biomarker used to gauge GH secretagogue efficacy. Analogs: IGF-1 LR3, IGF-1 Des, mecasermin.

IGF-1 DES(1-3)

Deleting the first three amino acids of IGF-1 cripples IGFBP binding while preserving receptor activity — giving DES(1-3) roughly 10× the in vitro potency of native IGF-1 at promoting cell growth in IGFBP-rich environments. Encyclopedia entry

IGF-1 LR3

IGF-1 rebuilt so its binding proteins barely hold it: more potent than IGF-1 in rats, cleared faster, and never given to a person in a published study. Encyclopedia entry

Immunogenicity

The tendency of a therapeutic protein or peptide to provoke an immune response. A major concern for biologics and some peptides, especially after repeated dosing. Humanized or fully-human sequences reduce immunogenicity.

Incretin

Gut hormones (GLP-1 and GIP) that enhance insulin secretion after meals. The 'incretin effect' is why oral glucose triggers more insulin than IV glucose at matched blood levels. GLP-1 agonists harness this mechanism.

IND

Investigational New Drug. FDA authorization allowing clinical trial use of an unapproved drug. Research peptides may be IND-authorized at academic centers but not available commercially.

Injection Site Reaction

Redness, swelling, itching or a lump where a drug was injected. Common with many injected peptides: EGRIFTA SV's label reports injection-site reactions in 25% of patients against 14% on placebo. A persistent lump needs medical attention.

INN

International Nonproprietary Name. The generic name assigned by WHO (e.g., semaglutide). Stem-based — '-glutide' endings identify GLP-1 analogs; '-pressin' identifies vasopressin analogs; '-relix' identifies GnRH antagonists.

Insulin aspart

Novo Nordisk's rapid-acting insulin analogue (NovoLog / NovoRapid, approved 2000): one amino-acid change at B28 brings its peak to 40–50 minutes after injection, against 80–120 for regular human insulin. Fiasp (2017) adds niacinamide and L-arginine for faster early absorption, and US biosimilars followed from 2025. Encyclopedia entry

Insulin degludec

Novo Nordisk's ultra-long-acting insulin (Tresiba, 2015) — forms soluble multi-hexamers in SC tissue that slowly dissociate for a >42-hour half-life and a flat, forgiving dosing window; the basal insulin with the lowest hypoglycemia risk profile. Encyclopedia entry

Insulin degludec / liraglutide (IDegLira)

Insulin degludec and liraglutide in one daily pen at a fixed ratio: more HbA1c lowering than either alone, with a boxed thyroid warning. Encyclopedia entry

Insulin detemir

Novo Nordisk's fatty-acid-acylated basal insulin (Levemir, 2005) — the myristoyl chain enables reversible albumin binding, extending the half-life; Novo Nordisk announced global discontinuation in December 2023 (US supply ended 2024). Encyclopedia entry

Insulin efsitora alfa

Lilly's once-weekly basal insulin, an insulin variant fused to an antibody Fc fragment, FDA-approved in September 2026 as Onswik for adults with type 2 diabetes after four QWINT trials found HbA1c lowering non-inferior to daily basal insulin. Encyclopedia entry

Insulin glargine

The dominant once-daily basal insulin for two decades (Lantus, Sanofi, 2000) — the pI-shift design causes microprecipitation in subcutaneous tissue for a nearly peakless 24-hour absorption profile; Toujeo (U-300) is the same molecule at 3× concentration. Encyclopedia entry

Insulin glargine / lixisenatide (iGlarLixi)

Sanofi's fixed-ratio insulin/GLP-1 combo pen (Soliqua, FDA 2016) — 100 units/mL insulin glargine + 33 mcg/mL lixisenatide; a parallel to Xultophy, differentiated by using short-acting prandial-biased lixisenatide rather than liraglutide. Encyclopedia entry

Insulin glulisine

Sanofi's rapid-acting insulin analog (Apidra, 2004) — the third rapid-acting analog approved, differentiated by being zinc-free in formulation, which gives it slightly faster monomeric onset than lispro or aspart. Encyclopedia entry

Insulin icodec

The first once-weekly basal insulin: better HbA1c than daily insulin in type 2 diabetes, nearly double the serious hypos in type 1. Encyclopedia entry

Insulin lispro

The first FDA-approved rapid-acting insulin analog (Humalog, Lilly, 1996) — the B28–B29 position swap prevents hexamer self-association, producing faster subcutaneous absorption than regular human insulin. Encyclopedia entry

Insulin Syringe

A small-volume syringe (typically 0.3, 0.5, or 1.0 mL) with a fixed or detachable short needle (27G–31G, 5–13mm), calibrated in insulin units. The standard tool for peptide subcutaneous injections.

Intradermal (ID)

Injection into the dermis (skin layer just below epidermis), at a shallow angle with very little volume. Used for some GHK-Cu mesotherapy protocols and tuberculin skin tests.

Intramuscular (IM)

Injection directly into muscle tissue. Faster absorption than subcutaneous, used for some peptides at higher volumes (hCG, HGH) or when faster onset is desired. Typically 1-inch, 22–25G needle.

Intranasal

Administration via nasal spray, providing direct CNS access through olfactory and trigeminal pathways. Semax, Selank, DSIP, and some oxytocin preparations are commonly intranasal.

Intraperitoneal (IP)

Injection into the peritoneal cavity — a research-only route in rodent pharmacology studies. Not used in humans.

Ipamorelin

A ghrelin-receptor agonist that released growth hormone without raising cortisol in pigs; in people it has one dosing study and a phase 2 surgery trial that found no benefit. Never approved. Encyclopedia entry

IU (International Unit)

A unit of biological activity (not mass), used primarily for hCG, growth hormone preparations, and insulin. Not interchangeable with mcg/mg without the compound's specific conversion factor.

K

Kappa Opioid Receptor

One of three classical opioid receptors (mu, delta, kappa). Activated primarily by dynorphin. Unlike mu receptors, kappa activation produces dysphoria rather than euphoria, making kappa agonists non-addictive but associated with unpleasant side effects.

Kisspeptin

A hypothalamic peptide upstream of GnRH, governing the reproductive axis. Kisspeptin-10 and Kisspeptin-54 are used in reproductive endocrinology and fertility research.

Kisspeptin-10

A short active fragment of human kisspeptin — under active clinical investigation for hypothalamic amenorrhea, infertility, and low libido in men and women. Encyclopedia entry

Kisspeptin-54

The full-length 54-amino-acid kisspeptin, the peptide that drives GnRH release. Its furthest-developed use is a single injection to trigger egg maturation in IVF: eggs matured in 95% of 60 women at high risk of ovarian hyperstimulation syndrome, with no moderate or worse case. Investigational, and prohibited in sport. Encyclopedia entry

Klotho Peptide

The kidney protein whose shed form circulates in blood and works with FGF23 on mineral balance, sold online as a longevity peptide. No published trial has given klotho to a person: human studies measure it, and 24 weeks of supervised exercise in 144 young adults did not move it. Research only. Encyclopedia entry

KN056

Alphamab's GLP-1 / glucagon dual agonist — an early-clinical Chinese entry in the GLP-1/glucagon mechanism space pioneered by cotadutide and now represented by pemvidutide and survodutide. Encyclopedia entry

KPV

A tripeptide from the tail of α-MSH: anti-inflammatory in mouse colitis and cell studies, never tested in people, and recommended for compounding by FDA's advisers in July 2026. Encyclopedia entry

KR-12

KRIVQRIKDFLR — the minimal 12-residue bactericidal fragment of LL-37. Retains selective antimicrobial activity while losing LL-37's host-cell toxicity, making it the canonical template for LL-37-derived antimicrobial peptide drug discovery. Research-only. Encyclopedia entry

L

Lactoferricin

An antimicrobial peptide from mother's milk — a potent cationic fragment of lactoferrin with broad-spectrum activity against bacteria, fungi, viruses, and parasites, plus emerging anticancer properties. Encyclopedia entry

Langlenatide

A weekly-to-monthly exendin-4-based GLP-1 agonist with positive Phase 3 cardiovascular outcomes (AMPLITUDE-O, 2021) — Sanofi returned the license to Hanmi in 2020; Hanmi re-partnered with Innovent in 2020 for China development and with Kailera in 2024 for global development. Encyclopedia entry

Lanreotide

A long-acting somatostatin analogue injected every 28 days, sold as Somatuline Depot for acromegaly, gastroenteropancreatic neuroendocrine tumours and carcinoid syndrome. In the 204-patient CLARINET trial it more than halved the risk of progression or death, with 65% progression-free at 24 months against 33% on placebo. Encyclopedia entry

Larazotide

An oral tight-junction regulator peptide (AT-1001) tested in coeliac disease: it eased symptoms at some doses but never changed its permeability marker, and its phase 3 trial was terminated by the sponsor in 2022. Not approved. Encyclopedia entry

Lean Body Mass (LBM)

Total body weight minus fat mass. Includes muscle, bone, water, and organs. GH secretagogue protocols target LBM preservation or gain; muscle-sparing agents (bimagrumab, apitegromab) specifically protect LBM during weight loss.

Leuphasyl

A cosmetic-ingredient pentapeptide modeled on leucine-enkephalin — marketed by Lipotec as a post-synaptic adjunct to Argireline-class pre-synaptic peptides for expression-line reduction. Encyclopedia entry

Leuprolide

The prototypical long-acting GnRH agonist: after a brief flare it shuts down testosterone and oestrogen, FDA-approved since 1985 in forms from a daily pen to six-month depots for prostate cancer, endometriosis, fibroids and central precocious puberty. Encyclopedia entry

LH

Luteinizing Hormone. Pituitary gonadotropin triggering ovulation and stimulating testicular testosterone production. Lutropin-alfa is the recombinant therapeutic form.

Ligandrol (LGD-4033)

Not a peptide. A SARM (selective androgen receptor modulator) studied in early clinical trials for muscle wasting and never approved. Commonly sold alongside peptides. WADA-prohibited.

Linaclotide

An oral peptide that works inside the bowel, approved for IBS with constipation and for constipation from the age of two. Encyclopedia entry

Lipidation

Attachment of a lipid group (fatty acid, cholesterol, palmitic acid) to a peptide. Extends half-life via albumin binding (acylation) or enhances skin penetration in cosmetic formulations (palmitoyl-peptides).

Lipodystrophy

Changes in fat tissue (atrophy or hypertrophy) at injection sites from repeated injections in the same spot. Prevented by systematic site rotation.

Liraglutide

The first once-daily GLP-1 analog to be FDA-approved for both type 2 diabetes (Victoza) and chronic weight management (Saxenda). Encyclopedia entry

Livagen

A Khavinson tetrapeptide proposed to support hepatic and lymphocyte function; reported to decondense chromatin in aged lymphocytes in in-vitro studies — Russian-language evidence, no Western replication. Encyclopedia entry

Lixisenatide

A short-acting, prandial GLP-1 agonist primarily used to target postprandial glucose excursions. Encyclopedia entry

Lixivaptan

An oral vasopressin V2 blocker, not a peptide, that raised sodium in hyponatraemia trials and was discontinued in June 2022. Encyclopedia entry

LL-37

The only human cathelicidin — an antimicrobial peptide with direct activity against bacteria, fungi, viruses, and biofilms, with additional roles in wound healing and immune signaling. Encyclopedia entry

Loading Phase

An initial period of higher or more frequent dosing to rapidly reach therapeutic concentration. TB-500 protocols often include a 4-week loading phase before maintenance.

Lonapegsomatropin

Ascendis Pharma's once-weekly growth hormone prodrug (Skytrofa) — the first weekly GH to receive FDA approval (August 2021) for pediatric GH deficiency in patients aged 1+ years weighing at least 11.5 kg. Encyclopedia entry

Luer Lock vs. Luer Slip

Two syringe-needle connection types. Luer-lock twists securely (safer for high-pressure or viscous injections); luer-slip simply presses in (simpler, cheaper). Insulin syringes usually use fixed needles — neither luer type.

Lutetium-177 DOTATATE

A targeted radiotherapy peptide — a somatostatin analog armed with a radioactive warhead that delivers lethal radiation directly to neuroendocrine tumor cells expressing sst2 receptors. Encyclopedia entry

Lutropin alfa

Recombinant human LH, given with FSH rather than alone; its largest trial found the endpoints comparable either way. Encyclopedia entry

Lyophilization

The freeze-drying process converting peptide solutions into stable powder. Peptide is frozen, then vacuum-dried to remove water while preserving molecular structure — why peptide powder is called 'lyophilized.'

M

Macimorelin

An orally active ghrelin receptor agonist FDA-approved in 2017 as a diagnostic test for adult growth hormone deficiency — the only oral alternative to the insulin tolerance test. Encyclopedia entry

Magainin

The frog-skin peptide that launched antimicrobial peptide research — discovered in 1987 when a researcher noticed surgical frogs never developed infections. Encyclopedia entry

Maintenance Phase

The period following a loading phase where dosing is reduced to a level that sustains therapeutic effect. Typically involves lower doses or less frequent administration.

Maridebart cafraglutide

Amgen's once-monthly obesity injection — Phase 3 MARITIME program underway, ~20% weight loss at 52 weeks in Phase 2 (NEJM 2025), approximately 21-day half-life enabling monthly or less frequent dosing. Encyclopedia entry

Mass Spectrometry (MS)

An analytical technique measuring the mass-to-charge ratio of molecules, confirming peptide identity and purity. Modern COAs typically include MS data alongside HPLC.

Matrikine

Peptide fragments from extracellular matrix proteins that signal remodeling. Palmitoyl-tripeptide-38 (Matrixyl 3000), palmitoyl-pentapeptide-4 (Matrixyl), and palmitoyl-tripeptide-5 are cosmetic matrikine peptides.

Mazdutide

The first dual glucagon and GLP-1 agonist approved for weight loss anywhere, by China in June 2025; not approved in the US. Encyclopedia entry

Mecasermin

Ipsen's recombinant human IGF-1 (Increlex) — FDA-approved in 2005 for severe primary IGF-1 deficiency; the direct replacement for IGF-1 in patients whose own IGF-1 production is inadequate despite normal GH levels. Encyclopedia entry

Mecasermin rinfabate

IGF-1 delivered bound to its carrier protein: approved in 2005 as iPlex, now listed as discontinued in the US. Encyclopedia entry

Melanocortin

Peptide hormones derived from POMC (pro-opiomelanocortin), including α-MSH, β-MSH, γ-MSH, and ACTH. PT-141 (bremelanotide), Melanotan II, Afamelanotide, and Setmelanotide act at melanocortin receptors.

Melanotan II

An unapproved melanocortin agonist sold as a tanning and libido injection, with small 1990s trials and case reports of changing moles, melanoma, priapism and kidney injury. Encyclopedia entry

Melatonin

The pineal darkness signal: an unregulated supplement in the US, a prescription prolonged-release medicine for insomnia in Europe. Encyclopedia entry

Melittin

The main weapon in bee venom — a powerful membrane-disrupting peptide being repurposed as an antimicrobial and anticancer research tool. Encyclopedia entry

Membrane Disruption

A mechanism by which antimicrobial peptides (AMPs) kill pathogens by destabilizing and permeabilizing their cell membranes. Unlike conventional antibiotics that target specific enzymes, membrane disruption makes resistance harder to develop.

MEN 2 (Multiple Endocrine Neoplasia Type 2)

A genetic syndrome (RET mutation) predisposing to medullary thyroid carcinoma and other endocrine tumors. An absolute contraindication to all GLP-1 receptor agonists and incretin mimetics.

Menotropin

The urine-derived FSH and LH preparation used for IVF ovarian stimulation, still about equal to recombinant FSH in trials. Encyclopedia entry

MGF

The IGF-1 splice variant muscle makes after loading, sold online as a synthetic fragment that has never been given to a person in a study. Encyclopedia entry

MHRA

Medicines and Healthcare products Regulatory Agency. The UK's drug regulator, operating independently post-Brexit. MHRA approves or rejects drugs separately from EMA since 2021.

Micrograms (mcg/µg)

One-millionth of a gram; 1 mg = 1,000 mcg. Many peptide doses are written in micrograms, so confusing mcg with mg is a thousand-fold error.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of an antimicrobial agent that prevents visible growth of a microorganism. A key metric for evaluating antimicrobial peptides (AMPs); lower MIC values indicate greater potency against the target pathogen.

Mitochondrial-Derived Peptide (MDP)

A peptide encoded by mitochondrial DNA rather than nuclear DNA. Humanin, MOTS-c and the small humanin-like peptides (SHLPs) are examples; most of what is known about them comes from cell and animal studies.

MK-677

An oral, non-peptide ghrelin-receptor agonist: it raised growth hormone and IGF-1 for months in trials and added lean mass in older adults, but failed in Alzheimer's and hip-fracture recovery, raised blood sugar and was never approved. Encyclopedia entry

Mod GRF 1-29

A short-acting GHRH analog — chemically identical to CJC-1295 but without the DAC albumin-binding linker — producing discrete GH pulses rather than sustained elevation. Encyclopedia entry

Molecular Formula

A notation specifying the exact count of each atom type in a molecule (e.g., BPC-157 = C62H98N16O22). Used alongside molecular weight to characterize a peptide's chemical identity.

Molecular Weight (MW)

The sum of atomic weights in a molecule, measured in daltons (Da) or g/mol. Used to characterize peptide size and to calculate mole-based dosing.

Monoclonal Antibody (mAb)

An engineered protein binding a single target with high specificity. Not a peptide — but often grouped with peptides in trial pipelines. Bimagrumab, trevogrumab, apitegromab, and garetosmab are mAbs in the myostatin/activin pathway.

MOTS-c

A mitochondrially encoded peptide studied for its effects on metabolic homeostasis, insulin sensitivity, and exercise capacity. Encyclopedia entry

Mounjaro

Eli Lilly's brand name for tirzepatide indicated for type 2 diabetes (FDA-approved 2022). Same molecule as Zepbound (the obesity-indication brand). Weekly subcutaneous injection.

mTOR

Mechanistic Target of Rapamycin. A master regulator of cell growth integrating nutrient, energy, and growth-factor signals. Peptides affecting IGF-1 (via GH secretagogues) indirectly activate mTOR signaling.

Mu Opioid Receptor

The primary opioid receptor responsible for analgesia, euphoria, and respiratory depression. Activated by beta-endorphin endogenously and by morphine/fentanyl exogenously. The main target for pain-relief peptide research.

Myostatin

A TGF-β family protein (GDF-8) that limits skeletal muscle growth. Myostatin inhibitors include follistatin, ACE-031, bimagrumab, apitegromab, trevogrumab, garetosmab, and taldefgrobep-alfa.

N

N-Terminus

The end of a peptide chain with a free amino (–NH2) group. Peptide sequences are written N-terminus first (left). N-terminal modifications (acetylation, pyroglutamate) are common for stability.

NA-Selank Amidate

Selank with an acetyl cap and an amide end. Sellers claim better stability and nasal absorption; no study of this form has been published. Encyclopedia entry

NAD+

Not a peptide. Nicotinamide Adenine Dinucleotide — an essential cellular coenzyme marketed by longevity clinics as an injectable or IV therapy. Sold alongside peptides; systemic absorption and cellular uptake pharmacology remain debated.

Nafarelin

Pfizer's Synarel, a GnRH agonist nasal spray approved for endometriosis and central precocious puberty: a depot-free alternative to injectable leuprolide for patients who prefer nasal dosing. Encyclopedia entry

Natriuretic Peptide

Peptides (ANP, BNP, CNP, urodilatin) produced by the heart and kidney that promote sodium excretion and vasodilation. Nesiritide, carperitide, and ularitide are natriuretic-peptide therapeutics.

Nausea

The most common side effect of GLP-1 medicines. In the labels' trials it affected 44% of people on Wegovy against 16% on placebo, and 25% to 29% on Zepbound against 8%, mostly during dose escalation.

Navepegritide

The weekly achondroplasia treatment — a PEGylated CNP prodrug approved in 2026 that provides continuous growth plate stimulation with once-weekly dosing. Encyclopedia entry

NDA

New Drug Application. The FDA pathway for approval of a small molecule or peptide drug. Requires Phase 3 data demonstrating safety and efficacy. GLP-1 analogs are NDA-approved (distinct from biologics, which use BLA).

NDI

New Dietary Ingredient. A supplement ingredient introduced after 1994 requires FDA NDI notification under DSHEA. Peptides marketed as 'dietary supplements' without NDI approval are technically misbranded.

Nesiritide

Recombinant human B-type natriuretic peptide, sold in the US as Natrecor for acute heart failure. In the 7,141-patient ASCEND-HF trial it did not change death or readmission and had only a small, non-significant effect on breathlessness; Drugs@FDA lists Natrecor as discontinued. Encyclopedia entry

Neuropeptide

A peptide functioning as neurotransmitter or neuromodulator. Endorphins, oxytocin, and substance P are natural; Semax, Selank, P21, and DSIP are synthetic neuropeptides.

Neuropeptide Y

The brain's most abundant neuropeptide — a 36-amino-acid master regulator of appetite, stress resilience, and anxiety that connects metabolic and cognitive peptide networks. Encyclopedia entry

Neurotensin

A gut-brain peptide that modulates dopamine transmission, pain sensitivity, and fat absorption — linking metabolic health to schizophrenia and addiction research. Encyclopedia entry

NF-κB

Nuclear Factor kappa-B. A transcription factor governing inflammation and immune response. Many peptides (e.g., KPV, thymosin alpha-1) modulate NF-κB signaling to temper inflammation.

Nisin

The food-grade antimicrobial peptide — a 34-amino-acid lantibiotic used in food preservation worldwide for 50+ years, with emerging pharmaceutical applications against MRSA and biofilms. Encyclopedia entry

Nitric Oxide (NO) System

A signalling system governing vasodilation, inflammation and tissue repair. Animal studies of BPC-157 report interactions with NO signalling.

NMN

Not a peptide. Nicotinamide mononucleotide, a small-molecule NAD+ precursor sold as a supplement and often stocked by peptide sellers.

Nociception

The sensory nervous system's process of detecting and transmitting pain signals. Several peptides modulate nociception — endogenous opioid peptides inhibit it, while substance P and CGRP amplify it. Ziconotide blocks nociceptive calcium channels.

Nonapeptide

A peptide containing exactly 9 amino acids. Oxytocin, vasopressin, desmopressin, and atosiban are nonapeptides (all oxytocin/vasopressin family).

Noopept

A Russian capped-dipeptide nootropic (omberacetam) with rodent memory data, two small open human studies, and a habit of turning up in US supplements. Encyclopedia entry

Nootropic Peptide

A peptide promoted for effects on memory, focus or learning. Semax and Selank are approved in Russia, not the US; the others sold under the label are research compounds, and the key paper on dihexa was retracted.

Norditropin

Novo Nordisk's brand of somatropin (recombinant human growth hormone), given with a prefilled pen.

NPAS3 Research Peptide

A research-only peptide derived from the NPAS3 (neuronal PAS domain protein 3) basic helix-loop-helix PAS transcription factor. NPAS3 has been linked to schizophrenia and cognitive phenotypes in human genetic studies, but the peptide itself has no clinical development. No human trials, no established dosing, and no substantiated therapeutic use. Encyclopedia entry

NPH insulin (isophane)

The classical intermediate-acting insulin — regular human insulin co-crystallized with protamine to produce ~12-hour action; still widely used for cost reasons despite being largely superseded by analog basal insulins for T1DM. Encyclopedia entry

O

Octapeptide

A peptide containing exactly 8 amino acids. Angiotensin II, SNAP-8 (cosmetic), and acetyl octapeptide-3 are octapeptides.

Octreotide

The first-generation somatostatin analog (FDA-approved as Sandostatin, 1988) — the pharmacological counterweight to growth-hormone excess. Used for acromegaly, carcinoid syndrome, and VIPoma; now available in injectable, LAR-depot, and oral (Mycapssa, 2020) formulations. Encyclopedia entry

Omiganan

An indolicidin-derived cationic antimicrobial peptide developed as a topical gel over two decades. Its catheter-infection phase 3 trials (completed 2003, and CLIRS, 2005–2008) missed their primary endpoints, and its 2015–2017 rosacea phase 3 programme produced one positive and one negative trial. Never approved. Encyclopedia entry

Opioid Peptide

A class of endogenous peptides that bind opioid receptors (mu, delta, kappa) to modulate pain, reward, and stress. Includes beta-endorphin, enkephalins, and dynorphins. Synthetic analogs target these pathways for analgesia.

Oral

Taken by mouth. Most peptides are broken down in the gut; the few oral peptide medicines rely on special engineering, such as the SNAC absorption enhancer in semaglutide tablets. Orforglipron and MK-677 are oral, but they are not peptides.

Oral Peptide

A peptide made to be swallowed. Semaglutide tablets rely on the SNAC absorption enhancer; icotrokinra and enlicitide are engineered cyclic peptides. Non-peptide pills such as orforglipron and MK-677 are a different category.

Orexin

A hypothalamic peptide (orexin A and B) regulating arousal, wakefulness, and appetite. Loss of orexin signaling causes narcolepsy type 1.

Orexin System

A neuropeptide signaling system involving orexin-A and orexin-B (also called hypocretin-1 and -2). Regulates wakefulness, appetite, and reward. Orexin deficiency causes narcolepsy. Both agonists and antagonists are in clinical development.

Orexin-A

The hypothalamic wakefulness peptide — loss of orexin neurons causes narcolepsy, and blocking its receptors produced the blockbuster insomnia drugs suvorexant and lemborexant. Encyclopedia entry

Orexin-B

The second orexin isoform — a 28-amino-acid peptide that preferentially activates the OX2 receptor most critical for maintaining wakefulness. Encyclopedia entry

Orforglipron

Not a peptide: an oral small-molecule GLP-1 receptor agonist, FDA-approved on April 1, 2026 as Foundayo for weight management; at its top dose it cut weight 11.2% over 72 weeks in ATTAIN-1, against 2.1% on placebo. Encyclopedia entry

Orphan Drug Designation

FDA status for drugs treating rare diseases (<200,000 US patients). Confers 7-year market exclusivity plus tax credits. Several peptides (setmelanotide, teduglutide, palovarotene) have orphan designations.

Orphan Peptide

Informal term for peptides with FDA orphan drug designation — approved or in development for rare diseases. Setmelanotide (rare obesity syndromes) and teduglutide (short bowel syndrome) are examples.

Ostarine (MK-2866)

Not a peptide. A SARM studied in phase 2 trials for muscle wasting and never approved. Widely sold alongside peptides. WADA-prohibited.

Ovagen

A Khavinson tripeptide proposed to support hepatocyte function and reproductive-tissue aging; evidence is Russian-language and pre-clinical. Encyclopedia entry

Over-the-Counter (OTC)

Available without a prescription. No therapeutic peptides for injection are OTC in the US. Topical cosmetic peptides, oral collagen peptides, and some bioregulator-like supplements are sold OTC.

Oxytocin

A 9-amino-acid neuropeptide produced in the hypothalamus. Drives uterine contraction, milk let-down, and social bonding. Carbetocin is a long-acting analog; atosiban is the antagonist.

Ozempic

Novo Nordisk's brand of semaglutide for type 2 diabetes (FDA-approved 2017). Weekly 0.25 – 2 mg subcutaneous injection. Same molecule as Wegovy (the obesity-indication brand) and Rybelsus (oral form).

P

P21

A CNTF-derived research peptide (Institute for Basic Research, New York) that crosses the blood-brain barrier and stimulates hippocampal neurogenesis in rodent models of Alzheimer disease, Down syndrome, and aging. Not FDA-approved; not commercially marketed; research-only with no human trials to date. Encyclopedia entry

Pal-GHK

The palmitoylated form of the GHK tripeptide (distinct from GHK-Cu) — widely used as a cosmetic ingredient in combination with Matrixyl (Matrixyl 3000 is Pal-GHK + Pal-KTTKS) for fine-line reduction. Encyclopedia entry

Palmitoyl Hexapeptide-12

Biopeptide EL — a palmitoyl-VGVAPG elastin "spring fragment" peptide. The VGVAPG sequence is chemotactic for fibroblasts and binds the elastin receptor complex (GLB1 / cathepsin-A / NEU-1); cosmetic firmness claims rest mostly on manufacturer data. Encyclopedia entry

Palmitoyl Pentapeptide-4

The palmitoylated procollagen fragment sold as Matrixyl (pal-KTTKS): in a 12-week split-face trial in 93 women a moisturiser containing it reduced wrinkles more than the same moisturiser alone. A cosmetic ingredient, not a drug. Encyclopedia entry

Palmitoyl Tetrapeptide-7

The anti-inflammatory partner in Matrixyl 3000 — a lipopeptide that reduces IL-6 and glycation damage in aging skin. Encyclopedia entry

Palmitoyl Tripeptide-38

Sederma's Matrixyl Synthe'6 — a palmitoyl tripeptide (Pal-KMO2K) claimed to stimulate six dermal-matrix components (collagens I / III / IV, fibronectin, hyaluronic acid, laminin-5). Follow-on to Matrixyl and Matrixyl 3000; almost all efficacy data is manufacturer-generated. Encyclopedia entry

Palmitoyl Tripeptide-5

Syn-Coll / Pal-KVK — a palmitoyl tripeptide modeled on the thrombospondin-1 motif that activates latent TGF-β. Mechanistically distinct from Matrixyl-family matrikines: activates a growth-factor signalling pathway rather than directly mimicking collagen fragments. Cosmetic ingredient only. Encyclopedia entry

Pancreatitis

Inflammation of the pancreas. Listed as a possible adverse event with GLP-1 agonists since early post-marketing reports, though large meta-analyses have not confirmed a causal link.

Pasireotide

The somatostatin analog for Cushing's disease — the only FDA-approved medical therapy targeting pituitary ACTH secretion, with uniquely broad somatostatin receptor affinity. Encyclopedia entry

PB-718

PegBio's dual GLP-1 / GLP-2 agonist — an unusual combination targeting both the incretin axis and intestinal mucosal trophic signaling; Phase 2 in T2DM and NAFLD. Encyclopedia entry

PCAC

Pharmacy Compounding Advisory Committee, the FDA advisory body that reviews bulk drug substances for compounding. In July 2026 it voted on a group of peptides; FDA had not acted on its votes as of September 30, 2026. Our PCAC hub has the votes.

PE-22-28

A short peptide that selectively blocks the TREK-1 potassium channel — studied in animal models as a fast-acting antidepressant candidate. Encyclopedia entry

PEG-MGF

A pegylated fragment of a proposed muscle-specific IGF-1 splice variant — the underlying "MGF" biology remains scientifically contested, and PEG-MGF itself has no human clinical data. Encyclopedia entry

Pegvisomant

Pfizer's GH receptor antagonist (Somavert) — FDA-approved in 2003 for acromegaly; important to distinguish from GH agonists because it does the opposite (blocks GH action rather than supplementing it). Encyclopedia entry

PEGylation

Attachment of polyethylene glycol chains to a peptide, extending half-life, reducing immunogenicity, and shielding from proteolysis. PEG-MGF and lonapegsomatropin are examples of PEGylated peptides.

Pemvidutide

Altimmune's GLP-1 / glucagon co-agonist — received FDA Breakthrough Therapy Designation for MASH in January 2026 after positive IMPACT Phase 2b antifibrotic data, with Phase 3 initiation planned for 2026. Encyclopedia entry

Pentadecapeptide

A peptide of exactly 15 amino acids. BPC-157 is a pentadecapeptide with the sequence Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val.

Pentapeptide

A peptide containing exactly 5 amino acids. Thymopentin, leu-enkephalin, and palmitoyl pentapeptide-4 are pentapeptides.

Pentapeptide-3

Vialox — the "curare-mimetic" cosmetic peptide (GPRPA). Acts post-synaptically on peripheral nicotinic ACh receptors, unlike the pre-synaptic SNAP-25-mimetic Argireline class. Sometimes marketed as a snake-venom-inspired Botox alternative; efficacy data are primarily from the manufacturer. Encyclopedia entry

Peptibody

A biologic molecule combining a peptide sequence with an antibody Fc domain, creating a longer half-life than the peptide alone. Romiplostim is the most well-known peptibody — a TPO receptor agonist fused to IgG1 Fc for weekly dosing.

Peptide

A short chain of amino acids (typically 2–50) linked by peptide bonds. Chains longer than ~50 amino acids or ~5,000 daltons are generally classified as proteins, though the boundary is conventional rather than absolute.

Peptide Bond

The covalent bond between the carboxyl group of one amino acid and the amino group of the next, formed via condensation (releasing water). The fundamental linkage in all peptides and proteins.

Peptide Hormone

A hormone made of amino acids (as opposed to steroid or amine hormones). Insulin, glucagon, GH, oxytocin, ADH, gonadotropins, and all hypothalamic releasing hormones are peptide hormones.

Peptide YY

The postprandial 'stop eating' signal — an endogenous satiety peptide that reduces appetite via the Y2 receptor, and a pharmacological target for next-generation obesity drugs. Encyclopedia entry

Peptidomimetic

A small molecule or modified peptide designed to reproduce a natural peptide's activity while resisting enzymatic degradation. MK-677 (ibutamoren) mimics ghrelin without being a peptide.

Petrelintide

Zealand's weekly amylin analogue, built to mix with other drugs and tested alone in a 42-week phase 2 obesity trial. Encyclopedia entry

Pexiganan

A synthetic 22-amino-acid analogue of the frog-skin peptide magainin 2, tested as a 1% cream against oral ofloxacin in two phase 3 trials in 835 people with mildly infected diabetic foot ulcers; about 85-90% improved on either. Never approved. Encyclopedia entry

Pharmacodynamics (PD)

What the drug does to the body — receptor binding, downstream signaling, dose-response relationships. Distinct from pharmacokinetics (what the body does to the drug).

Pharmacokinetics (PK)

How a compound is absorbed, distributed, metabolized, and eliminated. Key PK parameters: half-life, Cmax, Tmax, AUC, bioavailability, volume of distribution, clearance.

Pinealon

A Khavinson tripeptide proposed to cross the blood–brain barrier and support neuronal gene expression in aging brain tissue — animal data in hypoxia and oxidative stress models; no Western clinical trials. Encyclopedia entry

Pipeline Peptide

A peptide still in development and not yet approved, such as retatrutide, CagriSema (cagrilintide with semaglutide) and amycretin.

Plecanatide

A uroguanylin copy that draws water into the gut: approved as Trulance for chronic constipation and IBS-C, boxed warning under age 6. Encyclopedia entry

PNC-27

An experimental anticancer peptide engineered to selectively disrupt cancer cell membranes that overexpress HDM-2 — preclinical research only. Encyclopedia entry

Polymyxin B

The gram-negative last resort — a cyclic lipopeptide antibiotic revived from the 1950s as a critical weapon against carbapenem-resistant Acinetobacter, Pseudomonas, and Klebsiella. Encyclopedia entry

Polypeptide

A peptide chain of many amino acids (conventionally >20), often used interchangeably with 'peptide' or to describe a single polypeptide chain within a larger protein. GLP-1 (30 aa) and insulin (A-chain 21 aa, B-chain 30 aa) are polypeptides.

POMC

Pro-Opiomelanocortin. A precursor protein cleaved into ACTH, α-MSH, β-MSH, γ-MSH, β-endorphin, and β-lipotropin. Setmelanotide is used in rare POMC-pathway obesity syndromes.

PPAR

Peroxisome Proliferator-Activated Receptors (α, γ, δ). Nuclear receptors for fatty acids driving metabolic gene expression. Some peptides' metabolic effects converge on PPAR signaling.

Pramlintide

The amylin analog sold as Symlin from 2005 and now discontinued in the US — taken at mealtimes alongside insulin in T1D and T2D. The pharmacological proof-of-concept for amylin agonism that petrelintide and cagrilintide are now building on. Encyclopedia entry

Prescription Only

Available only via prescription from a licensed practitioner. FDA-approved peptides (all GLP-1 agonists, GH, desmopressin) are prescription-only. Compounded peptides similarly require a valid prescription to be legally dispensed.

Prodrug

An inactive compound metabolized into its active form in vivo. Lonapegsomatropin is a PEG-GH prodrug slowly releasing active somatropin; terlipressin is a vasopressin prodrug.

Prostamax

A Khavinson prostate bioregulator preparation marketed in Russia for prostate aging, with the synthetic KEDP tetrapeptide (Prostagen) as its characterized active fragment. Russian-language evidence base; no FDA/EMA status; no independent Western clinical replication. Encyclopedia entry

Protirelin

Synthetic thyrotropin-releasing hormone (pGlu-His-Pro-NH2), once FDA-approved as the pituitary diagnostics Thypinone (1976) and Thyrel TRH (1978), both now discontinued; tried experimentally in depression, ALS and preterm lung disease. Encyclopedia entry

PT-141

An FDA-approved melanocortin agonist for acquired, generalized hypoactive sexual desire disorder in premenopausal women. Encyclopedia entry

Pulsatile Dosing

Administering a drug in short pulses that mimic natural hormonal rhythms. Pulsatile GnRH treatment is used for hypogonadotropic hypogonadism to restore fertility.

R

Racemization

Conversion of L-amino acids into their D-isomers (or vice versa), often due to improper synthesis or storage. A quality-control issue in peptide manufacturing, since it can abolish biological activity.

RAD-140 (Testolone)

Not a peptide. A SARM investigated for androgen-receptor-mediated muscle and breast-cancer effects. Commonly sold on research-chemical sites alongside peptides. WADA-prohibited; associated with liver-toxicity case reports in misuse contexts.

Receptor

A protein on or inside a cell that binds a specific molecule (ligand) and triggers a biological response. Peptides work by binding specific receptors — GLP-1R, GHS-R, MC4R, and so on.

Receptor Downregulation

A protective reduction in receptor density after prolonged agonist exposure. The body's way of dampening chronic stimulation; a reason protocols include off-cycles.

Reconstitution

Dissolving lyophilized peptide powder in diluent to create an injectable solution. Proper technique — slow injection down the vial wall, gentle swirling (never shaking) — is critical for peptide integrity.

Regular human insulin

The original recombinant human insulin (Humulin R, 1982) — unmodified native sequence, short-acting kinetics driven by hexamer self-association; U-500 concentration for severely insulin-resistant patients. Encyclopedia entry

Relamorelin

A ghrelin-agonist pentapeptide for diabetic gastroparesis: positive phase 2 trials, then all five phase 3 trials terminated in 2020 on a business decision. Encyclopedia entry

Relugolix

The oral alternative to Lupron: a once-daily pill that takes testosterone to castrate levels in prostate cancer without the initial flare or injections of GnRH agonists, and, with add-back hormones, treats fibroids and endometriosis. Encyclopedia entry

Research Chemical

A product sold 'for research purposes only, not for human consumption.' The label does not make a product legal for people to take: FDA's August 2026 warning letters to five online peptide sellers said such labels did not outweigh websites showing the products were meant for human use.

Retatrutide

An investigational triple hormone agonist that produced ~24% weight loss at 48 weeks in Phase 2 — the largest in any single-agent obesity trial to date. Encyclopedia entry

Rigin

The anti-inflammatory partner in Matrixyl 3000 — a lipopeptide that reduces IL-6 and glycation damage in aging skin. Encyclopedia entry

Romiplostim

A peptibody that boosts platelet production — an Fc-fused peptide mimicking thrombopoietin, FDA-approved for immune thrombocytopenia. Encyclopedia entry

Rybelsus

Novo Nordisk's oral semaglutide tablet (FDA-approved 2019). Uses SNAC (sodium N-(8-[2-hydroxybenzoyl] amino) caprylate) as an absorption enhancer. Daily dosing, lower bioavailability than injectable forms.

S

S-23

Not a peptide. A SARM in early research for male contraception and muscle effects. Commonly sold alongside peptides; no human approval; WADA-prohibited.

Saturation

The dose at which a receptor is maximally occupied; increasing dose further produces no additional effect. In a 1994 study of hexarelin in healthy men, 2 µg/kg was already close to the maximum growth hormone response.

Saxenda

Novo Nordisk's brand of liraglutide for chronic weight management (FDA-approved 2014). Daily 3 mg subcutaneous injection. Same molecule as Victoza (the diabetes-indication brand).

Scenesse

Brand name for afamelanotide (Clinuvel Pharmaceuticals), FDA-approved 2019 for erythropoietic protoporphyria. A subcutaneous implant lasting ~2 months, providing skin pigmentation-based photoprotection.

Schedule III Controlled Substance

The DEA schedule for drugs with moderate abuse potential, which includes anabolic steroids.

Secretagogue

A substance that promotes the secretion of another. Growth hormone secretagogues (CJC-1295, Ipamorelin, Sermorelin) promote GH release.

Secretin

The first hormone ever discovered — a 27-amino-acid gut peptide that stimulates pancreatic bicarbonate secretion and opened the entire field of endocrinology in 1902. Encyclopedia entry

Selank

A Russian nasal anxiolytic built from the immune peptide tuftsin; its human evidence is small Russian trials that compare it with benzodiazepines, not placebo. Encyclopedia entry

Selective

Preferentially activating one receptor subtype over others. Ipamorelin is called selective because, in pigs, it released growth hormone without raising ACTH or cortisol, which GHRP-6 and GHRP-2 did; that has not been shown in a published human study.

Selectivity Index

The ratio of a compound's toxicity to host cells versus its activity against target cells or pathogens. For antimicrobial peptides, a high selectivity index means the peptide kills microbes at concentrations well below those that harm human cells.

Semaglutide

A once-weekly GLP-1 receptor agonist FDA-approved for type 2 diabetes and chronic weight management. Encyclopedia entry

Semax

A synthetic ACTH-derived heptapeptide approved in Russia for stroke rehabilitation and optic nerve disorders, with documented BDNF upregulation and broad nootropic activity. Encyclopedia entry

Senolytic

A compound that selectively kills senescent cells. FOXO4-DRI is a peptide senolytic designed to disrupt the FOXO4-p53 interaction, triggering apoptosis in senescent cells.

Sequence

The specific order of amino acids in a peptide chain, determining 3D structure and function. BPC-157's sequence is GEPPPGKPADDAGLV; semaglutide's is HAEGTFTSDVSSYLEGQAAKEFIAWLVRGRG with Aib at position 8.

Sermorelin

GHRH's first 29 amino acids, sold in the US as Geref (approved 1990 and 1997) to test and treat childhood growth hormone deficiency until it was discontinued, not for safety reasons. Encyclopedia entry

Setmelanotide

An MC4 receptor agonist peptide sold as Imcivree, approved in the US for obesity due to Bardet-Biedl syndrome or POMC, PCSK1 or LEPR deficiency (from age 2) and acquired hypothalamic obesity (from age 4). In hypothalamic obesity, BMI fell 16.5% against a 3.3% rise on placebo over 52 weeks. Encyclopedia entry

SHLP2

A 26-aa mitochondrial-derived peptide, the most-studied of the SHLP1–SHLP6 family (Cohen lab, USC). Preclinical data report insulin-sensitizing, antiapoptotic, and metabolic-protective effects; lower plasma levels in humans correlate with age and with type 2 diabetes. Research-only; no human clinical trials. Encyclopedia entry

SHLP6

One of six small humanin-like peptides encoded in mitochondrial DNA: its sequence is unusually conserved, and 2025 zebrafish studies reported antioxidant and neuroprotective effects. Research-only. Encyclopedia entry

Signal Peptide

A short amino acid sequence (typically 15–30 residues) at the N-terminus of a newly synthesized protein that directs it to the secretory pathway. Also used colloquially in cosmetics to describe peptides that stimulate collagen or elastin production.

Site Rotation

Systematically changing injection locations to prevent lipodystrophy, scar tissue, and localized irritation. Common scheme: rotate between left/right abdomen, thighs, and upper arms on a daily or weekly basis.

SLU-PP-332

Not a peptide. An estrogen-related receptor agonist described in 2023 as an 'exercise mimetic' in rodent studies. WADA added it to its Prohibited List for 2027.

SNAP-8

The 'Super Argireline' — an extended SNAP-25 fragment peptide that reduces expression wrinkles without injections. Encyclopedia entry

Somapacitan

Novo Nordisk's once-weekly growth hormone (Sogroya) — FDA-approved in 2020 for adult GH deficiency and in 2023 for pediatric GH deficiency in children aged 2.5+ years. Encyclopedia entry

Somatostatin

A hypothalamic peptide that inhibits GH release, insulin, glucagon, and many GI hormones. Octreotide and lanreotide are synthetic somatostatin analogs.

Somatrogon

Pfizer/OPKO's once-weekly growth hormone (Ngenla) — FDA-approved in June 2023 for pediatric GH deficiency in children aged 3+ years; uses a CTP-fusion strategy borrowed from long-acting follitropin alfa. Encyclopedia entry

Somatropin (HGH)

FDA-approved recombinant human growth hormone — the direct hormone replacement, with multiple clinical indications, prescription-only status, and specific federal criminal provisions against off-label distribution. Encyclopedia entry

SPPS

Solid-Phase Peptide Synthesis. Merrifield's 1963 technique for assembling peptides one amino acid at a time on a resin bead. The dominant method for manufacturing research and pharmaceutical peptides today.

SR9009 (Stenabolic)

Not a peptide. A Rev-Erb agonist small molecule studied for circadian and metabolic effects. Very poor oral bioavailability; effects in humans largely unvalidated. Sold by research-chemical vendors alongside peptides.

SS-31 (Elamipretide)

The first FDA-approved mitochondria-targeted peptide therapeutic — approved September 2025 as Forzinity for Barth syndrome, with broader investigation in heart failure, macular degeneration, and aging. Encyclopedia entry

Steady State

The point at which elimination matches intake, yielding stable blood concentrations. Typically reached after 4–5 half-lives of repeated dosing. For semaglutide, steady state takes 4–5 weeks.

Sterile Water (SWFI)

Sterile Water For Injection. Preservative-free sterile water. Used for one-time-use reconstitution of peptides that will be injected immediately; not recommended for multi-dose storage (no antibacterial preservative).

Subcutaneous (SubQ)

Injection into the fat layer beneath the skin, the usual route for injected peptides, typically with a short insulin needle in the abdomen, thigh or upper arm.

Sublingual

Administration under the tongue. Mucosal absorption avoids GI breakdown and first-pass metabolism for some peptides (BPC-157 sublingual exists as a product format), though evidence is generally weaker than for injection.

Substance P

The pain neuropeptide of the NK1 receptor: infusing it gave 71% of healthy adults a headache, and blocking it failed as a painkiller. Encyclopedia entry

Survodutide

A once-weekly glucagon/GLP-1 dual agonist: about 13% weight loss at 76 weeks in phase 3 and MASH improvement in phase 2, but not yet approved anywhere. Encyclopedia entry

Syn-Ake

A "snake-venom mimetic" cosmetic tripeptide modeled on Waglerin-1 (Tropidolaemus wagleri venom) — blocks post-synaptic acetylcholine receptors rather than acting pre-synaptically like Argireline; modest reductions in expression-line depth in manufacturer studies. Encyclopedia entry

T

Tabimorelin

Novo Nordisk's oral growth hormone secretagogue (NN703): GH rose in healthy men, but not beyond placebo in GH-deficient adults, and it inhibits CYP3A4. Discontinued. Encyclopedia entry

Tachyphylaxis

Rapid loss of response to repeated dosing, usually within hours or days. Distinct from long-term tolerance. Melanotan II users often report tachyphylaxis-like effects on appetite suppression.

Taldefgrobep alfa

Biohaven's anti-myostatin adnectin-Fc fusion: its Duchenne programme ended in 2019 after a futility analysis, and its phase 3 RESILIENT trial in SMA missed its primary endpoint in November 2024. Encyclopedia entry

Taspoglutide

A once-weekly GLP-1 RA co-developed by Ipsen and Roche — Phase 3 halted in 2010 after unacceptably high rates of injection-site reactions and hypersensitivity (including systemic allergic reactions), making it the most prominent immunogenicity-driven failure in the GLP-1 class. Encyclopedia entry

TB-500

A synthetic fragment of thymosin β4 studied in animal models for actin-binding-mediated tissue repair, particularly in cardiac and soft-tissue injury. Encyclopedia entry

Teduglutide

FDA-approved GLP-2 analog (Gattex/Revestive, 2012) for short-bowel syndrome — the first disease-modifying treatment for SBS, reducing parenteral nutrition dependence by promoting intestinal mucosal growth. Encyclopedia entry

Telomerase

An enzyme that extends telomeres (DNA caps at chromosome ends), counteracting natural telomere shortening during cell division. Epithalon is studied for telomerase activation.

Telomere

Protective DNA-protein caps at chromosome ends that shorten with each cell division. Telomere length is a biomarker of cellular aging; Epithalon targets telomere maintenance.

Teriparatide

The first 34 amino acids of parathyroid hormone, injected at 20 micrograms once a day to build bone. Approved as Forteo for osteoporosis at high fracture risk: in the 1,360-woman VERO trial, new spine fractures occurred in 5.4% against 12.0% on risedronate over two years. Fracture-healing trials found no clear benefit. Encyclopedia entry

Terlipressin

Terlivaz — the first and only FDA-approved drug for hepatorenal syndrome (HRS). FDA-approved September 2022 (Mallinckrodt) for adults with HRS with rapid reduction in kidney function, after a multi-decade regulatory history including four prior Complete Response Letters and the successful CONFIRM Phase 3 trial (NEJM 2021). Encyclopedia entry

Tesamorelin

An FDA-approved GHRH analog for reducing excess visceral fat in HIV-associated lipodystrophy. Encyclopedia entry

Tesofensine

A triple monoamine reuptake inhibitor, not a peptide: 9 to 11% more weight loss than placebo at 24 weeks in phase 2, a faster heart rate, a ten-day half-life, and no approval anywhere. Encyclopedia entry

Testagen

A Khavinson testis bioregulator; its synthetic form, the tetrapeptide KEDG, is named testagen in a 2025 paper. Russian nutraceutical status only. Encyclopedia entry

Tetrapeptide

A peptide containing exactly 4 amino acids. Acetyl tetrapeptide-5, acetyl tetrapeptide-2, and tetrapeptide-3 (cosmetic) are tetrapeptides. The Khavinson tetrapeptides (e.g., Cortagen, Epitalon) are longevity bioregulators.

TFA

Trifluoroacetic acid. A common residue from peptide synthesis and HPLC purification. Some peptide preparations are further purified to remove TFA due to toxicity concerns in chronic dosing.

TGA

Therapeutic Goods Administration. Australia's drug regulator. TGA has a particularly strict stance on peptides — many research peptides are classified Schedule 4 (prescription-only) or Schedule 9 (prohibited).

TGF-β Superfamily

A large family of cytokines including TGF-βs, activins, BMPs, myostatin (GDF-8), GDF-11, and GDF-15. Many pipeline peptides/biologics target this family — follistatin, apitegromab, bimagrumab, trevogrumab.

Thrombopoietin (TPO)

A hormone that regulates platelet production by stimulating megakaryocyte growth. Romiplostim (Nplate) is an FDA-approved peptibody (peptide-Fc fusion) TPO receptor agonist used to treat chronic immune thrombocytopenia.

Thymalin

A polypeptide mixture extracted from calf thymus, injected as an immune modulator and approved in Russia. Its human studies are small, mostly Russian and usually add it to other treatment; in a non-randomised COVID-19 comparison, hospital mortality was 20.6% with thymalin against 40.9% on standard care. Not approved in the US. Encyclopedia entry

Thymic Peptide

Peptides originating from or mimicking thymus-gland products, typically immunomodulatory. Thymosin alpha-1, thymulin, thymopentin, and thymalin are thymic peptides.

Thymogen

L-glutamyl-L-tryptophan, a synthetic dipeptide developed in the Soviet Union and used in Russia as an immunomodulator; its evidence is small, mostly uncontrolled Russian-language studies and one double-blind surgical trial. No FDA or EMA approval. Encyclopedia entry

Thymopentin

A synthetic five-amino-acid fragment of thymopoietin (TP-5), sold as Timunox. Small 1980s and 1990s trials found modest benefits over placebo in atopic dermatitis and rheumatoid arthritis. Not approved in the US. Encyclopedia entry

Thymosin α1

A thymic peptide approved as Zadaxin in about 35 countries; its hepatitis trials were mixed, and its largest trial, in 1,106 sepsis patients, found no effect on death. Encyclopedia entry

Thymosin β4

The body's main actin-sequestering peptide, 43 amino acids long: tested as eye drops (RGN-259) for dry eye and corneal wounds, and not the short TB-500 fragment. Encyclopedia entry

Thymulin

A zinc-dependent thymic nonapeptide, measured in people far more often than it has ever been given to them. Encyclopedia entry

Tirzepatide

A once-weekly GLP-1/GIP dual agonist that produced unprecedented weight loss in SURMOUNT trials — up to ~21% at highest dose. Encyclopedia entry

Titration

Gradually increasing dose to improve tolerability. GLP-1 agonists are standardly titrated over 12–20 weeks to reduce GI side effects. Starting doses are sub-therapeutic by design.

Tmax

Time to maximum concentration. Sermorelin (~8 min), BPC-157 (~15 min subcutaneously), and semaglutide (~24 hr) illustrate the range for peptide therapeutics.

Topical

Applied to the skin. The primary route for cosmetic peptides (Matrixyl, Argireline, GHK-Cu, SNAP-8). Topical peptides usually require a lipidation group (palmitoyl-) for stratum corneum penetration.

Transdermal

Delivery through the skin into systemic circulation — distinct from topical (local action). Very few peptides work transdermally due to molecular size; patches and microneedle arrays are active research areas.

Trevogrumab

⚠ Monoclonal antibody — not a classical peptide. A Regeneron anti-myostatin fully human IgG (~150 kDa) being tested as a muscle-sparing adjunct to GLP-1 therapy — CONVERGE combination program with semaglutide in obesity; earlier sarcopenia programs were deprioritized in favor of the obesity opportunity. Included here because it's widely discussed alongside peptides in muscle-sparing conversations. Encyclopedia entry

Tripeptide

A peptide containing exactly 3 amino acids. GHK (glycyl-histidyl-lysyl), KPV (lysyl-prolyl-valyl), TRH, and glutathione (γ-Glu-Cys-Gly) are tripeptides.

Tripeptide-10 Citrulline

The INCI name for the active peptide in Decorinyl® — a tetrapeptide (KDI-Cit) whose charge pattern (+/−/0/+) reproduces decorin's collagen-binding motif. Decorinyl is the trade name of this molecule; both names lead to this entry. Encyclopedia entry

Triple Agonist

A single molecule activating three receptors. Retatrutide (GLP-1/GIP/glucagon) and HM15275 (GLP-1/GIP/glucagon) target three incretin/metabolic pathways in one compound, producing the largest weight-loss signals to date in trials.

Triptorelin

A widely used long-acting GnRH agonist — FDA-approved as Trelstar for advanced prostate cancer and as Triptodur for pediatric central precocious puberty; approved internationally (Decapeptyl, Gonapeptyl) for endometriosis, uterine fibroids, and female infertility protocols. Encyclopedia entry

Trough Level

The lowest blood concentration between doses, occurring just before the next dose. Monitoring trough levels helps determine if dosing frequency sustains therapeutic effect.

Trulicity

Eli Lilly's brand of dulaglutide (GLP-1/Fc fusion) for type 2 diabetes (FDA-approved 2014). Weekly 0.75–4.5 mg subcutaneous injection in a pre-filled auto-injector.

U

U-100

The calibration of standard insulin syringes: 100 units = 1 mL, so 10 units = 0.1 mL. Units measure volume, not the amount of drug.

Ularitide

⚠ Phase 3 failure. Cardiorentis's ularitide, a synthetic copy of the kidney's natriuretic peptide urodilatin, lowered cardiac filling pressures in phase 2, but TRUE-AHF (NEJM 2017, n=2,157) found no effect on cardiovascular death or on the early clinical course. Never approved. Encyclopedia entry

Upregulation

An increase in the number or sensitivity of cellular receptors, typically in response to a signalling molecule. In a cell study, BPC-157 increased growth hormone receptor expression in tendon fibroblasts.

Urofollitropin

Ferring's Bravelle (and earlier Fertinex) — highly purified urinary-derived FSH used for ovulation induction and IVF controlled ovarian stimulation. FDA-approved 2002; branded Bravelle was withdrawn from the US market in 2015 due to manufacturing/potency concerns but the molecule class remains available via urinary-derived menotropin combination products. Encyclopedia entry

USP <797>

United States Pharmacopeia chapter 797. Standards for sterile pharmaceutical compounding, covering environment, technique, and beyond-use dating. Compounding pharmacies must follow USP <797> for sterile peptide preparations.

USP <800>

United States Pharmacopeia chapter 800. Standards for handling hazardous drugs (cytotoxic, reproductive hazard, teratogenic). Some compounded peptide preparations in oncology/endocrinology settings trigger USP <800> handling.

V

Vancomycin

The IV antibiotic for resistant staphylococci and the oral one for C. difficile, now dosed by drug levels and beaten head-to-head by newer drugs. Encyclopedia entry

Vasopressin

The antidiuretic hormone as an ICU vasopressor (Vasostrict, 2014): added to norepinephrine in shock, it was safe but did not lower mortality in VASST or pooled trials, did better after cardiac surgery, and its price rose steeply after a 2014 rebranding. Encyclopedia entry

Vasopressin (ADH)

Antidiuretic Hormone. A 9-amino-acid posterior pituitary peptide regulating water reabsorption and vascular tone. Desmopressin, terlipressin, and felypressin are synthetic analogs.

VEGF

Vascular endothelial growth factor, a signalling protein that promotes new blood vessel growth. Animal and cell studies of BPC-157 report effects on VEGF receptor signalling.

Ventfort

A Khavinson bioregulator made from bovine vascular tissue, sold in Russia for vascular aging. No published sequence or PubMed record names it. Encyclopedia entry

Vesugen

The synthetic KED tripeptide in the Khavinson short-peptide series, studied preclinically for vascular-aging and antiatherogenic effects. Not a registered medicine; research-only in the West, nutraceutical status in Russia. Preclinical evidence only. Encyclopedia entry

Vial

The small glass container holding lyophilized peptide, sealed with a rubber stopper and aluminum flip-cap. Standard sizes: 2mL, 5mL, 10mL. Peptide quantity (mg) and vial size are independent — a 5mg peptide may ship in a 2mL vial.

Victoza

Novo Nordisk's brand of liraglutide for type 2 diabetes (FDA-approved 2010). Daily 0.6–1.8 mg subcutaneous injection. Same molecule as Saxenda.

VIP

Vasoactive Intestinal Peptide. A 28-amino-acid neuropeptide/hormone with broad vasodilatory, immunomodulatory, and smooth-muscle relaxing actions. A member of the secretin/glucagon/GHRH peptide family.

Visoluten

The Khavinson retinal bioregulator preparation, marketed in Russia for age-related retinal change including macular degeneration support. Evidence base is Russian-language Khavinson-group studies. Not FDA- or EMA-approved. Encyclopedia entry

VK2735

Viking's emerging dual GLP-1/GIP agonist — Phase 2 SC data in obesity reported up to ~14.7% placebo-adjusted weight loss at 13 weeks (VENTURE, 2024), with an oral-tablet Phase 2 program initiated 2024; the principal clinical challenger to tirzepatide's mechanism outside the Lilly / Novo axis. Encyclopedia entry

Volume of Distribution (Vd)

A theoretical volume representing how extensively a drug distributes outside the plasma. Large Vd suggests heavy tissue binding; small Vd suggests a drug largely confined to blood. Peptides vary widely.

Vosoritide

The first drug approved for achondroplasia — a CNP analog that stimulates endochondral bone growth by counteracting overactive FGFR3 signaling. Encyclopedia entry

Vyleesi

Brand name for bremelanotide (PT-141), FDA-approved 2019 for hypoactive sexual desire disorder in premenopausal women. On-demand subcutaneous auto-injector.

W

WADA

World Anti-Doping Agency, which maintains the Prohibited List for sport. Growth hormone and its releasing factors, EPO and many research peptides are prohibited at all times; GLP-1 medicines are not prohibited but are monitored.

Washout Period

Time off a drug to clear it before restarting or switching. Community 'cycling' protocols include washouts on the idea of restoring sensitivity; few have been tested.

Wegovy

Novo Nordisk's brand of semaglutide for chronic weight management (FDA-approved 2021): a weekly injection with a usual maintenance dose of 2.4 mg, and daily tablets. Same molecule as Ozempic and Rybelsus.

Withdrawn

A drug removed from the market after approval, for safety, efficacy or commercial reasons. Albiglutide (Tanzeum), a GLP-1 medicine, was discontinued by its maker for commercial reasons.

Y

YK-11

Not a peptide. A steroidal compound often marketed as a SARM, with a myostatin-inhibitor-adjacent mechanism that remains debated. Sold alongside peptides on research-chemical sites; WADA-prohibited; no human clinical development.

Z

Zepbound

Eli Lilly's brand name for tirzepatide indicated for chronic weight management (FDA-approved 2023). Same molecule as Mounjaro (diabetes-indication brand). Weekly subcutaneous injection.

Ziconotide

A cone snail venom peptide turned FDA-approved painkiller — the first non-opioid intrathecal analgesic for severe chronic pain. Encyclopedia entry

Zilucoplan

A self-injectable complement inhibitor — a synthetic macrocyclic peptide that blocks C5 complement activation, FDA-approved for generalized myasthenia gravis as a daily subcutaneous injection. Encyclopedia entry