Ipamorelin
Sold as the 'clean' growth hormone peptide: its selectivity was shown in pigs, its one human efficacy trial found no benefit, and FDA lists it as a compounding safety risk
Ipamorelin is a five-amino-acid peptide from Novo Nordisk's 1990s growth hormone programme that switches on the ghrelin receptor. In pigs it released growth hormone without raising ACTH or cortisol, the result behind its reputation as the selective GHRP. In people it has been tested in one dosing study and one phase 2 trial, in bowel surgery patients, which found no benefit over placebo. It was never approved, and FDA placed it in Category 2 for 503B compounding in 2023, citing immunogenicity and a published report of serious adverse events including death.
What is it?
Ipamorelin is a pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, that emerged in the late 1990s from a Novo Nordisk chemistry programme built on GHRP-1: the team removed that peptide's central alanine-tryptophan pair and kept the growth hormone activity. It acts on the ghrelin receptor, the same receptor as GHRP-6, GHRP-2, hexarelin and ibutamoren. Its development code was NNC 26-0161.
Its reputation comes from one result in pigs. In the 1998 discovery paper, ipamorelin released growth hormone about as potently as GHRP-6 in rat pituitary cells, anaesthetised rats and conscious pigs, but unlike GHRP-6 and GHRP-2 it did not raise ACTH or cortisol in the pigs, even at doses more than 200 times what it took to release growth hormone. None of the peptides tested changed prolactin, FSH, LH or TSH. That selectivity has not been measured in a published human study that we could find.
The human record is short. In 1999, 40 healthy men given a single 15-minute intravenous infusion had one pulse of growth hormone peaking at about 40 minutes, and ipamorelin itself had a half-life of about 2 hours. In 2014, a phase 2 trial gave 114 bowel-surgery patients intravenous ipamorelin or placebo twice daily to speed recovery of gut function; the time to the first tolerated meal was 25.3 hours against 32.6 on placebo, a difference that was not significant. It was never approved for any use.
Most of the rest is rodent work: longer bones and more bone mineral in rats, protection against steroid-induced muscle weakness, faster gut transit after abdominal surgery. FDA placed ipamorelin acetate in Category 2 of its 503B compounding policy on September 29, 2023, citing a risk of immune reactions from aggregation or impurities, its unnatural amino acids and a published report of serious adverse events including death when it was given intravenously for gastric motility. Its 503A nomination was withdrawn.
Mechanism of Action
Ipamorelin mimics ghrelin at its receptor. The growth hormone release has been measured in people; the hormonal selectivity, the bone effects and the gut effects come from animals.
Selectivity was shown in pigs and the growth hormone pulse in healthy men. Its only patient trial missed its endpoints, and no trial has tested it for body composition.
Each step is tagged with where it was shown. A dashed red arrow marks a link the evidence does not establish.
The pathway in words
- Ipamorelin. A five-amino-acid peptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, from a chemistry programme on growth hormone-releasing peptides. Shown in: lab. Source: PubMed 9849822.
- The ghrelin-type receptor. In rat pituitary cells it released growth hormone as potently as GHRP-6, and antagonist tests placed its action on the GHRP receptor. Shown in: cells. Source: PubMed 9849822.
- Growth hormone only. In pigs it did not raise ACTH or cortisol, even at over 200 times its effective dose, where GHRP-6 and GHRP-2 did. Shown in: animals. Source: PubMed 9849822.
- One pulse in men. In 40 healthy men given infusions at five dose levels, growth hormone peaked once at about 40 minutes; ipamorelin's half-life was 2 hours. Shown in: people. Source: PubMed 10496658.
- tested, no benefit shown. Faster bowel recovery. In 114 patients after bowel surgery, time to a tolerated meal was 25.3 against 32.6 hours (p = 0.15), with no significant difference on any endpoint. Shown in: people. Source: PubMed 25331030.
Ghrelin receptor: growth hormone
In rat pituitary cells ipamorelin released growth hormone with a potency close to GHRP-6's, and blocking experiments showed it works through the GHRP receptor. In healthy men, a single infusion produced one pulse of growth hormone that peaked at about 40 minutes and then fell away, with a response at every dose tested.
Selectivity: shown in pigs
In conscious pigs, GHRP-6 and GHRP-2 raised ACTH and cortisol, and ipamorelin did not, even at more than 200 times its effective growth hormone dose. None of the three changed prolactin, FSH, LH or TSH. The human dosing study measured only growth hormone, so whether the selectivity holds in people has not been published.
Gut motility
As a ghrelin mimetic, ipamorelin sped the first bowel movement and gastric emptying in rats after abdominal surgery, and restored the contractility of stomach muscle strips. In the one human trial of that idea, patients recovering from bowel resection did not tolerate food significantly sooner than on placebo.
Bone and muscle in rats
Given to rats for weeks, ipamorelin increased longitudinal bone growth and bone mineral content, partly by making bones larger rather than denser, and it counteracted the fall in muscle strength and bone formation caused by high-dose glucocorticoids. None of these effects has been tested in people.
Published Research
Our evidence set returned 40 papers that name ipamorelin, 16 of them in their titles. The 14 cards below are three human studies, ten animal studies and one laboratory study. Only two of the human papers tested the drug in patients or volunteers; the third was an anti-doping method paper with one volunteer per compound. Our dataset also cited a 2014 'phase 3' trial in J Gastrointest Surg; PubMed has no such paper, and the only trial of ipamorelin in bowel surgery by that author is the 2014 phase 2 study carded below, so that citation was replaced.
Dosing and growth hormone in 40 men
Healthy men received one 15-minute intravenous infusion at one of five doses (4.21 to 140.45 nmol/kg), eight men per dose. Ipamorelin's kinetics were dose-proportional, with a terminal half-life of 2 hours. Each dose produced a single episode of growth hormone release peaking at 0.67 hours and declining to negligible levels, with half-maximal stimulation at a concentration of 214 nmol/L.
Phase 2: bowel recovery after surgery
In a multicentre, double-blind trial, 114 adults having small or large bowel resection received intravenous ipamorelin (0.03 mg/kg) or placebo twice daily for up to seven days. Median time to the first tolerated solid meal was 25.3 hours on ipamorelin and 32.6 on placebo (p = 0.15), and no secondary efficacy measure differed. Adverse events occurred in 87.5% on ipamorelin and 94.8% on placebo; the authors call the drug well tolerated.
How doping labs detect it
To build an anti-doping test, researchers gave one volunteer each a nasal dose of GHRP-1, GHRP-2, GHRP-6, hexarelin or ipamorelin and analysed urine for two days. Ipamorelin was heavily metabolised, and its fragment ipamorelin (1–4) free acid was still detectable after the parent peptide had disappeared from urine; the method was validated for routine testing.
Discovery: selective in pigs
Ipamorelin released growth hormone from rat pituitary cells and in anaesthetised rats with potency and efficacy similar to GHRP-6, and did so in conscious pigs at an ED50 of 2.3 nmol/kg. In the pigs, GHRP-6 and GHRP-2 raised ACTH and cortisol, but ipamorelin did not, even at more than 200-fold its ED50; none of the peptides changed FSH, LH, prolactin or TSH.
Kinetics in rats, and through the nose
In rats, ipamorelin's plasma clearance was five times lower than GHRP-6's, and unlike GHRP-6, which left mainly in bile, it was excreted mainly in urine, largely intact. Given into the nose, about 20% was absorbed, compared with about 50% for GHRP-2.
Faster bone growth in rats
Adult female rats injected three times daily for 15 days grew their tibias faster in a dose-dependent way, from 42 µm a day on vehicle to 52 µm a day at the highest dose, and gained weight. IGF-1, its binding proteins and bone turnover markers did not change, and the growth hormone response to a test dose of ipamorelin was marginally reduced afterwards.
More bone mineral, larger bones
Young adult female rats given ipamorelin, GHRP-6 or growth hormone by pump for 12 weeks gained body weight and bone mineral content. The gain came from larger bones rather than denser ones: bone mineral corrected for body weight and volumetric bone density were unchanged.
Against steroid-induced weakness
Adult female rats given the glucocorticoid methylprednisolone for three months lost muscle strength and bone formation. Adding ipamorelin (100 µg/kg three times daily) increased the calf muscles' maximum tension and raised the periosteal bone formation rate fourfold compared with the steroid alone.
Pituitary cells after 21 days
In young female rats treated with ipamorelin for 21 days, pituitary growth hormone cells showed more secretion granules and lower basal growth hormone content in culture, and only cells from these rats responded to ipamorelin, GHRP-6 or GHRH with more growth hormone cells and higher content. The authors read this as dynamic control of the growth hormone cell population.
Postoperative ileus in rats
After abdominal surgery in rats, a single intravenous dose of ipamorelin (1 mg/kg) shortened the time to the first bowel movement, and repeated doses over two days increased faecal output, food intake and weight gain. The authors suggested intravenous ipamorelin might help patients with postoperative ileus.
Stomach emptying after surgery
In rats with surgically delayed gastric emptying, 78% of a test meal remained in the stomach on vehicle and 52% after intravenous ipamorelin (0.014 µmol/kg), against 44% in rats without surgery. Ipamorelin and ghrelin also reversed the loss of contractility in stomach muscle strips taken after surgery.
Weight loss on chemotherapy in ferrets
In ferrets given the chemotherapy drug cisplatin, ipamorelin (1–3 mg/kg into the abdomen) did not reduce acute or delayed vomiting, but it reduced the related weight loss by about 24% in the delayed phase, as did anamorelin, another ghrelin-receptor agonist.
Appetite and testes in tilapia
Male tilapia given 5 or 30 µg of ipamorelin acetate for 21 days ate more and had more developing sperm cells, higher luteinizing hormone and 11-ketotestosterone in blood, and more androgen receptor protein at the higher dose, with no change in hypothalamic GnRH fibres.
Insulin release from rat pancreas
In pancreatic tissue fragments from normal and diabetic rats, ipamorelin increased insulin secretion. Blockers of calcium channels and of adrenergic receptors inhibited the effect, which the authors attribute to those two pathways.
What people say, and what was measured
Ipamorelin is sold on its selectivity: it releases growth hormone without the cortisol and prolactin that older secretagogues raise. That part is well documented. The company that owned it then ran a proper trial of the one use it was being developed for, and the drug did not beat placebo.
It releases growth hormone cleanly, without raising cortisol or prolactin like the older peptides.
Heard in: Grey Peptides listing review, October 1, 2026: listings present it as the selective secretagogue, contrasted with GHRP-6. Sellers are not named.
This is the finding the molecule was named for: it was described in 1998 as the first selective growth hormone secretagogue. In healthy men, a dose-ranging infusion study measured a single episode of growth hormone release peaking at 0.67 hours, dose-proportional kinetics, and a terminal half-life of about two hours. PMID: 9849822, 10496658
Tested in people; supportedIt speeds recovery and healing, which is why it is stacked with CJC-1295.
Heard in: Grey Peptides listing review, October 1, 2026: listings pair it with CJC-1295 for recovery and body composition. Sellers are not named.
No trial has tested recovery, healing or body composition in people. The one randomised controlled trial in humans tested something else entirely, and the supporting work on bone and tissue is in rats: longitudinal bone growth, bone mineral content in adult rats, and protection against steroid-induced bone loss. PMID: 10373343, 10828840, 11735244
Never tested in peopleIt works on the gut, which is why it helps digestion and appetite.
Heard in: Journal of Gastrointestinal Surgery, the proof-of-concept trial report of ipamorelin for bowel recovery after surgery, which is the clinical programme the gut claims trace to (read October 1, 2026). Source
It was tested for exactly this and missed. In a randomised placebo-controlled trial of ipamorelin 0.03 mg/kg twice daily for up to seven days after bowel surgery, median time to the first tolerated meal was 25.3 hours against 32.6 on placebo (p = 0.15), and there were no significant differences on the key or secondary efficacy analyses. The supporting motility work is in rodents. PMID: 25331030, 19289567, 27186127
Tested in people; not shownIt clears the body quickly, so it will not show up on a test.
Heard in: Grey Peptides listing review, October 1, 2026: listings note its short half-life. Sellers are not named.
The half-life is short, about two hours. Detection is a different question: an ipamorelin metabolite was found in urine after nasal administration of growth hormone releasing peptides, and remained detectable after the parent substance had cleared. PMID: 10496658, 25869809
Contradicted by the ruleEach claim is quoted from where it is said, never from a seller, and checked as of October 1, 2026 against the studies listed below.
Dosing Data
Ipamorelin has no approved dose. The human studies gave it into a vein: single infusions of 4.21 to 140.45 nmol/kg in healthy men (about 3 to 100 µg/kg), and 0.03 mg/kg twice daily for up to a week after bowel surgery. The flat doses in circulation are community figures with no trial behind them.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or 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.
→ Full Ipamorelin dosage guide — the community figures, the intravenous doses the human studies used, and why the two are hard to compare.
→ Blend & Stack Calculator — Ipamorelin is also sold in multi-peptide vials; the calculator shows what each draw delivers of every component; our blends and stacks hub sets out what each mix contains and what has been studied.
Side Effects & Contraindications
Reported Side Effects
Human safety data come from the 1999 dosing study and the 2014 phase 2 trial; FDA's 2023 Category 2 notice adds its own reading of the literature.
Contraindications & Cautions
No trial defined who should avoid ipamorelin. These cautions follow from what has and has not been studied.
Legal Status
Ipamorelin is not approved as a medicine anywhere. In the US it is in Category 2 of FDA's 503B compounding policy. Status as of September 26, 2026.
Frequently Asked Questions
?Does ipamorelin raise cortisol or prolactin?
Not in pigs. In the 1998 discovery study it released growth hormone without raising ACTH or cortisol, even at more than 200 times the effective dose, while GHRP-6 and GHRP-2 raised both; none of the three changed prolactin. The one published human dosing study measured only growth hormone, so the claim that it spares cortisol in people rests on the animal result.
?Has ipamorelin been tested in humans?
Twice, as far as we could find. A 1999 study gave single intravenous infusions to 40 healthy men and measured its kinetics and the growth hormone pulse it caused. A 2014 phase 2 trial gave it intravenously to 114 bowel-surgery patients and found no significant benefit over placebo. No trial has tested it under the skin, for weeks, or for body composition.
?What is ipamorelin's half-life?
About 2 hours in healthy men after an intravenous infusion, from the 1999 dosing study. The growth hormone pulse it causes is shorter, peaking at about 40 minutes after the start of the infusion and then declining to negligible levels.
?Why did FDA put ipamorelin in Category 2?
On September 29, 2023, FDA placed ipamorelin acetate in Category 2 of its 503B policy, the list of substances that may present significant safety risks in compounding. It cited possible immune reactions from aggregation or impurities, the complexity added by its unnatural amino acids, and a published report of serious adverse events including death with intravenous use for gastric motility.
?Is ipamorelin the same as ibutamoren (MK-677)?
No. Both act on the ghrelin receptor, but ipamorelin is an injected pentapeptide and ibutamoren is a small molecule taken by mouth. They are different drugs with different evidence.
?Why is ipamorelin combined with CJC-1295?
Because the two act on different receptors that both lead to growth hormone release: ipamorelin on the ghrelin receptor and CJC-1295 on the GHRH receptor. Studies of related peptides show synergy between the two pathways. No published trial has tested the ipamorelin and CJC-1295 combination in people.
References
- [pubmed] Gobburu JV, et al. "Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers." Pharm Res, 1999;16(9):1412-6. PMID: 10496658.
- [clinical-trial] Beck DE, et al. "Prospective, randomized, controlled, proof-of-concept study of the Ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients." Int J Colorectal Dis, 2014;29(12):1527-34. PMID: 25331030.
- [pubmed] Semenistaya E, et al. "Determination of growth hormone releasing peptides metabolites in human urine after nasal administration of GHRP-1, GHRP-2, GHRP-6, Hexarelin, and Ipamorelin." Drug Test Anal, 2015;7(10):919-25. PMID: 25869809.
- [pubmed] Raun K, et al. "Ipamorelin, the first selective growth hormone secretagogue." Eur J Endocrinol, 1998;139(5):552-61. PMID: 9849822.
- [pubmed] Johansen PB, et al. "Pharmacokinetic evaluation of ipamorelin and other peptidyl growth hormone secretagogues with emphasis on nasal absorption." Xenobiotica, 1998;28(11):1083-92. PMID: 9879640.
- [pubmed] Johansen PB, et al. "Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats." Growth Horm IGF Res, 1999;9(2):106-13. PMID: 10373343.
- [pubmed] Svensson J, et al. "The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats." J Endocrinol, 2000;165(3):569-77. PMID: 10828840.
- [pubmed] Andersen NB, et al. "The growth hormone secretagogue ipamorelin counteracts glucocorticoid-induced decrease in bone formation of adult rats." Growth Horm IGF Res, 2001;11(5):266-72. PMID: 11735244.
- [pubmed] Jiménez-Reina L, et al. "Influence of chronic treatment with the growth hormone secretagogue Ipamorelin, in young female rats: somatotroph response in vitro." Histol Histopathol, 2002;17(3):707-14. PMID: 12168778.
- [pubmed] Venkova K, et al. "Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus." J Pharmacol Exp Ther, 2009;329(3):1110-6. PMID: 19289567.
- [pubmed] Greenwood-Van Meerveld B, et al. "Efficacy of ipamorelin, a ghrelin mimetic, on gastric dysmotility in a rodent model of postoperative ileus." J Exp Pharmacol, 2012;4:149-55. PMID: 27186127.
- [pubmed] Lu Z, et al. "The growth hormone secretagogue receptor 1a agonists, anamorelin and ipamorelin, inhibit cisplatin-induced weight loss in ferrets: Anamorelin also exhibits anti-emetic effects via a central mechanism." Physiol Behav, 2024;284:114644. PMID: 39043357.
- [pubmed] Gouda M, et al. "The influence of ghrelin agonist ipamorelin acetate on the hypothalamic-pituitary-testicular axis in a cichlid fish, Oreochromis mossambicus." Anim Reprod Sci, 2024;268:107550. PMID: 38996787.
- [pubmed] Adeghate E, et al. "Mechanism of ipamorelin-evoked insulin release from the pancreas of normal and diabetic rats." Neuro Endocrinol Lett, 2004;25(6):403-6. PMID: 15665799.
- [other] U.S. Food and Drug Administration. Certain bulk drug substances for use in compounding that may present significant safety risks (ipamorelin acetate, 503B category 2 since September 29, 2023). Content current as of April 22, 2026; read September 26, 2026.
Sources & Citations
Every citation on this page is PubMed-indexed and has been checked against its record, except FDA's Category 2 page, which is cited as published. A citation in our earlier entry to a 2014 'phase 3' trial in J Gastrointest Surg matched no PubMed record and was replaced by the 2014 phase 2 trial it appears to describe. 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.