Morphiceptin
A milk-casein-derived opioid tetrapeptide and classic selective mu-receptor agonist — a pharmacology tool, not a drug
Morphiceptin is a four-amino-acid opioid peptide, Tyr-Pro-Phe-Pro-NH2, that comes from milk: it is the amidated first four residues of beta-casomorphin, the opioid fragment released from cow's-milk beta-casein. When it was characterized in 1981 it stood out for being a potent and unusually SELECTIVE agonist of the mu opioid receptor — the receptor through which morphine acts — with little activity at the delta or kappa receptors. That selectivity made morphiceptin a workhorse of opioid pharmacology: researchers have used it, and built countless analogs from it, to map how a short peptide engages the mu receptor and to design more stable or more potent mu-opioid ligands. It belongs to the same family of mu-selective opioid tetrapeptides as the endomorphins, and shares its milk-casein origin with beta-casomorphin-7. Morphiceptin is a research peptide and pharmacological tool; it is not an approved medicine and has not been given to people as a treatment.
No established human dose Details ↓
Recommended Dosing
No established human dose
Morphiceptin is a research opioid peptide; it has never been given to people as a treatment. The work is in receptor assays, cells and animals, where synthetic peptide or its analogs are used at experimental amounts that do not carry over to people.
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What is it?
Morphiceptin is a short opioid peptide with a tidy pedigree. Its sequence, Tyr-Pro-Phe-Pro-NH2, is simply the first four residues of bovine beta-casomorphin — the opioid peptide family released from cow's-milk beta-casein — capped with a C-terminal amide. So it is, in effect, beta-casomorphin-4 amide, a food-derived ('exorphin') opioid, and a close relative of beta-casomorphin-7.
Its importance comes from its receptor profile. When Chang and colleagues characterized morphiceptin in 1981, it proved to be a potent agonist that was remarkably selective for the mu opioid receptor — the morphine receptor — rather than the delta or kappa receptors. At a time when tools to distinguish the opioid-receptor subtypes were scarce, a small, mu-specific peptide was valuable, and morphiceptin became a standard mu-opioid ligand for receptor-binding and bioassay work.
Much of the subsequent literature is structure-activity chemistry. Because morphiceptin's activity depends on two aromatic residues (the tyrosine and phenylalanine) held in a particular geometry by its prolines, it has been an ideal scaffold for asking what a peptide must look like to engage the mu receptor. Studies replacing its proline spacer or its phenylalanine with mimetic residues showed a high degree of structural tolerance at the mu site — the key requirement is the right placement of the aromatic side chains, which the peptide can reach through different backbone conformations, including both cis and trans forms of the tyrosine-proline bond. This work overlaps closely with analog studies of endomorphin-2, the endogenous mu-selective tetrapeptide, which morphiceptin resembles.
Morphiceptin behaves as an opioid in functional tests. Its analogs and chimeras produce naloxone-reversible analgesia in mice, and combining the morphiceptin pharmacophore with a neuropeptide-FF-derived fragment yielded a chimeric peptide far more potent than either parent, acting through mixed mu/delta and NPFF-receptor mechanisms. Even in invertebrate neurons, morphiceptin (like met-enkephalin) modulated a GABA-activated current in a naloxone-sensitive way, illustrating the evolutionary reach of opioid-GABA interactions.
Throughout, morphiceptin is a research peptide and a pharmacological tool, and a milk-casein-derived opioid. No published study has given morphiceptin to people as a treatment, it is approved nowhere, and anything sold online under its name is an unregulated research chemical. Nothing here is a dose or a therapy; this page records what the published science says.
Mechanism of Action
Morphiceptin is a milk-casein-derived opioid tetrapeptide (beta-casomorphin-4 amide) that acts as a potent, highly selective agonist of the mu opioid receptor. Its activity depends on the placement of its two aromatic residues, making it a classic scaffold for mu-opioid structure-activity and analog design.
Selective mu-opioid agonism
A potent agonist selective for the mu (morphine) opioid receptor over delta and kappa; its analgesia is naloxone-reversible (PMIDs 6259732, 22960407).
Aromatic pharmacophore
Mu-receptor binding needs the right placement of its tyrosine and phenylalanine side chains, held by proline spacers that allow cis/trans backbone geometry (PMIDs 15857121, 20692738).
Food-casein origin
Derived from bovine beta-casein as the amide of beta-casomorphin-4, a food ('exorphin') opioid related to beta-casomorphin-7 (PMID 6259732).
Published Research
These are studies of morphiceptin read from their PubMed records on November 7, 2026: the 1981 discovery paper establishing it as a potent, selective mu-opioid agonist; structure-activity studies mapping its bioactive shape at the mu receptor (often alongside endomorphin-2 analogs); a chimeric-peptide analgesia study in mice; and a study of its opioid-GABA interaction in mollusc neurons. The evidence is in cells, receptors and animals; morphiceptin has not been given to people as a treatment.
Discovery: morphiceptin, a potent selective mu-opioid agonist
Morphiceptin (Tyr-Pro-Phe-Pro-NH2) was characterized as a potent and specific agonist for the mu (morphine) opioid receptor — selective over the delta and kappa receptors — establishing a small milk-casein-derived peptide as a valuable mu-specific pharmacological tool (the founding study).
Morphiceptin / endomorphin-2 analogs: mu binding and antinociception
Analogs of endomorphin-2 and morphiceptin with phenylalanine-mimic residues were synthesised and assessed; mu-opioid binding affinities were measured and selected analogs showed potent antinociceptive activity in the mouse hot-plate test, with brain-homogenate half-lives giving insight into their degradation — morphiceptin serving as a mu-selective scaffold (a preclinical study).
The bioactive shape of morphiceptin at the mu-receptor
Morphiceptin analogues with a dipeptide-mimetic replacing the terminal Xaa-Pro units revealed a high degree of structural tolerance at the mu-opioid binding site: the essential requirement is the location and orientation of the two aromatic side chains, which the peptide can reach through different backbone conformations and cis/trans Tyr-Pro configurations (a conformational study).
Proline-surrogate morphiceptin and endomorphin-2 analogs
Replacing the position-2 proline of morphiceptin and endomorphin-2 with beta-homologue and sulphonic-acid proline surrogates produced novel analogs; binding and functional assays characterised their mu-opioid affinity, including the first beta-sulphonamido analog in the opioid-peptide field — further structure-activity mapping of the mu-selective tetrapeptides (an in-vitro study).
A morphiceptin-based chimeric peptide with strong analgesia (mice)
A chimeric peptide (MCRT) built from morphiceptin and a neuropeptide-FF-derived fragment produced dose- and time-dependent analgesia in mice far exceeding either parent peptide; the effect was blocked completely by naloxone and involved mixed mu/delta opioid and NPFF-receptor mechanisms (a preclinical result showing morphiceptin's value as an analgesic scaffold).
Morphiceptin modulates a GABA current in neurons
In identified mollusc (Lymnaea) neurons, morphiceptin and met-enkephalin dose-dependently reduced or blocked GABA-activated chloride inward currents, with the reversible component being naloxone-sensitive — demonstrating an opioid-GABA interaction conserved across species and a postsynaptic action of morphiceptin (an electrophysiology study).
No Established Human Dose
Morphiceptin is a research opioid peptide; it has never been given to people as a treatment. The work is in receptor assays, cells and animals, where synthetic peptide or its analogs are used at experimental amounts that do not carry over to people. No regulator has approved any dose, and no published human dose exists, so no amount is printed here.
What this rests on: PMID 6259732, PMID 16682191, PMID 22960407.
Educational information, not medical advice. The doses on this page come from approved labels, published studies and, where no study exists, amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
What a Buyer Needs to Know
What is sold, how it is mixed, stored and taken, and what is known about its safety, quality and legal status. Each part names its source. Where we have none, it says unknown.
What is sold
Unknown: we hold no label and no published test that says what forms or vial sizes Morphiceptin is sold in. A vial's own label is a seller's claim, not a source.
Mixing a vial: a worked example
Unknown: no human dose of Morphiceptin has been established (see No Established Human Dose below), so there is no amount to work out. The reconstitution calculator does the arithmetic for any vial, water and dose.
Storage before and after mixing
Unknown: no label or published stability study on file says how to store Morphiceptin, before or after mixing. The mixing guide sets out the general rules, with their sources: keep a mixed vial in the fridge, and use it promptly, as the bacteriostatic water label says of any drug dissolved in it. The 28 days often quoted is the limit for an opened multiple-dose vial from a manufacturer, an outer limit set for sterility, not a time a mixed solution has been shown to keep. Nobody has published how long Morphiceptin stays intact once mixed.
How it is taken
Unknown: with no established human dose, there is no established way of taking Morphiceptin. What the human studies gave and how is set out under No Established Human Dose.
What to expect, and when
How long it stays in the body: a half-life of short; a small peptide degraded by brain and tissue peptidases. After about five half-lives almost none is left.
When effects appear: unknown; no source on this page gives a time to effect for Morphiceptin. Results reported in the studies are under Published Research.
Source: half-life: PMID 16682191.
Side effects, and when to stop or get help
From the Side Effects section: No human adverse-event data exist: no published study has administered morphiceptin to people; As a selective mu-opioid agonist, the class risks of mu-opioids (tolerance, dependence, respiratory depression, sedation) would be expected concerns — a mechanistic inference, not human data; Its analgesia in animals is naloxone-reversible, confirming opioid-receptor-mediated action (PMID 22960407); Material sold online as 'morphiceptin' is an unregulated research chemical of unverified content. Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping Morphiceptin. Treat a severe or unexpected reaction as a reason to stop and see a doctor.
Source: the Side Effects section below (“Morphiceptin is a research opioid peptide that has not been given to people as a drug, so there is no human safety profile; the points below reflect that research status and its opioid pharmacology”).
Interactions
Unknown: a PubMed search for human interaction studies of Morphiceptin (reviewed 2026-11-07) found none. Unknown is not the same as safe to combine.
Every peptide's record, with its source: the interaction matrix.
Checking what you bought
Unknown: no published independent test of Morphiceptin products is in our lab-results database yet, so how products sold under this name measure up is not known.
To read a certificate of analysis, paste it into the COA decoder. Trust & Verification explains what independent testing can and cannot show.
Legal status
US: Research Chemical (Not a drug: Drugs@FDA and the openFDA label endpoint hold no record, and FDA GSRS and ChEMBL hold no approved-drug record for morphiceptin (searched November 7, 2026)). Sport: Not on the 2026 List.
Country by country ↓ · Regulatory tracker
Source: this entry's approval status and the WADA Prohibited List, as in Legal Status below.
Side Effects & Contraindications
Reported Side Effects
Morphiceptin is a research opioid peptide that has not been given to people as a drug, so there is no human safety profile; the points below reflect that research status and its opioid pharmacology.
Contraindications & Cautions
Morphiceptin has no approved use and no label. These points reflect its research status.
Legal Status
Morphiceptin is a research opioid peptide (a milk-casein-derived beta-casomorphin amide); it is not a drug and is not approved in any country.
Frequently Asked Questions
?What is morphiceptin?
A four-amino-acid opioid peptide (Tyr-Pro-Phe-Pro-NH2) that is the amide of beta-casomorphin-4, from cow's-milk beta-casein. It is a potent, selective agonist of the mu (morphine) opioid receptor (PMID 6259732).
?Why is it important?
Its mu-selectivity made it a standard pharmacological tool for studying the mu-opioid receptor, and a scaffold for designing mu-opioid analogs — often alongside endomorphin-2 (PMIDs 15857121, 16682191).
?How does it relate to beta-casomorphin-7?
Both come from milk beta-casein: morphiceptin is the amidated first four residues of beta-casomorphin, while beta-casomorphin-7 is the seven-residue form. Both are food-derived ('exorphin') opioids.
?Is it approved or available to buy?
No. Morphiceptin is not a medicine, has no FDA application or label, and is approved nowhere. Material sold online as morphiceptin is an unregulated research chemical. Grey Peptides lists no sellers and recommends no source; this page records the published science.
References
- [mechanism] Chang KJ, et al. "Morphiceptin (NH4-tyr-pro-phe-pro-COHN2): a potent and specific agonist for morphine (mu) receptors." Science, 1981;212(4490):75-7. PMID: 6259732.
- [animal] Gao Y, et al. "Opioid receptor binding and antinociceptive activity of the analogues of endomorphin-2 and morphiceptin with phenylalanine mimics in the position 3 or 4." Bioorg Med Chem Lett, 2006;16(14):3688-92. PMID: 16682191.
- [mechanism] Grieco P, et al. "Morphiceptin analogues containing a dipeptide mimetic structure: an investigation on the bioactive topology at the mu-receptor." J Med Chem, 2005;48(9):3153-63. PMID: 15857121.
- [mechanism] Giordano C, et al. "Synthesis and activity of endomorphin-2 and morphiceptin analogues with proline surrogates in position 2." Eur J Med Chem, 2010;45(10):4594-600. PMID: 20692738.
- [animal] Li M, et al. "Analgesic properties of chimeric peptide based on morphiceptin and PFRTic-amide." Regul Pept, 2012;179(1-3):23-8. PMID: 22960407.
- [mechanism] Rózsa KS, et al. "Met-enkephalin and morphiceptin modulate a GABA-induced inward current in the CNS of Lymnaea stagnalis L." Gen Pharmacol, 1996;27(8):1337-45. PMID: 9304403.
- [other] Morphiceptin is the opioid tetrapeptide Tyr-Pro-Phe-Pro-NH2, the C-terminal amide of beta-casomorphin-4 (the first four residues of bovine beta-casomorphin, itself from milk beta-casein). It was characterized by Chang and colleagues in 1981 as a potent and selective mu-opioid-receptor agonist, as described in the discovery paper carded on this page (read November 7, 2026).
- [other] US FDA, Drugs@FDA and the openFDA label endpoint, searched November 7, 2026: no application and no label record for morphiceptin. It is a research opioid peptide (a milk-casein-derived beta-casomorphin amide), not a drug; FDA GSRS and ChEMBL hold no approved-drug record for it.
Sources & Citations
The six studies carded above were read from their PubMed records on November 7, 2026. Morphiceptin's structure (Tyr-Pro-Phe-Pro-NH2, beta-casomorphin-4 amide), its origin from bovine beta-casein, its potent selective mu-opioid agonism, its role as a structure-activity scaffold (with endomorphin-2), the chimeric MCRT analgesia, and the opioid-GABA interaction are from the discovery paper and studies carded here; the absence of US approval or a drug record from Drugs@FDA, openFDA, FDA GSRS and ChEMBL was checked the same day. Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.