Ipamorelin

01 · What it is

Ipamorelin is a synthetic pentapeptide, Aib-His-D-2-naphthylalanine-D-phenylalanine-Lys-NH2, and a selective agonist at the growth hormone secretagogue receptor GHS-R1a ³. It was characterised in 1998 by a group at Novo Nordisk under a title that states its whole claim: Ipamorelin, the first selective growth hormone secretagogue ³.

The selectivity is real and it is measurable. In conscious swine, ipamorelin released growth hormone with a potency close to GHRP-6 — ED50 2.3 ± 0.03 versus 3.9 ± 1.4 nmol/kg, Emax 65 ± 0.2 versus 74 ± 7 ng GH/mL — while GHRP-2 was more potent than either. What separated ipamorelin from both was what it did not do: unlike GHRP-6 and GHRP-2, it did not stimulate release of adrenocorticotropic hormone or cortisol ³. That is a genuine pharmacological advance and it is the honest case for this compound.

Whether the advance produces a clinical benefit was tested once. In a multicentre, double-blind, placebo-controlled phase 2 trial, 117 patients undergoing bowel resection received intravenous ipamorelin 0.03 mg/kg twice daily or placebo for up to seven days, for postoperative ileus. Median time to first tolerated meal was 25.3 hours on ipamorelin and 32.6 hours on placebo, p = 0.15. Treatment-emergent adverse events occurred in 87.5% of the ipamorelin group and 94.8% of placebo. The authors concluded that ipamorelin was well tolerated and that there were no significant differences between ipamorelin and placebo in the key and secondary efficacy analyses ⁵.

That is the entire controlled clinical record. The selectivity claim survives; the efficacy claim was tested and not supported.

As of September 2026 ipamorelin holds no marketing authorisation from any regulator.

02 · Evidence at a glance

Evidence grade

Early Clinical — one completed randomised trial, null on its endpoints

Structure

Synthetic pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2 ³

Molecular target

Growth hormone secretagogue receptor GHS-R1a ^3,4

Defining property

Selectivity — releases growth hormone without ACTH or cortisol, unlike GHRP-6 and GHRP-2 ³

Potency relative to GHRP-6

Comparable: ED50 2.3 vs 3.9 nmol/kg in conscious swine ³

Potency relative to GHRP-2

Lower; GHRP-2 more potent on growth hormone release ³

Randomised controlled trials

1, in postoperative ileus ⁵

Patients in that trial

117 enrolled, 114 analysed ⁵

Primary efficacy result

Median 25.3 vs 32.6 hours to first tolerated meal, p = 0.15 — not significant ⁵

Adverse events in that trial

87.5% ipamorelin vs 94.8% placebo ⁵

Trials in body composition, recovery or ageing

None

Approval status

None, any jurisdiction

03 · Mechanism of action

GHS-R1a agonism

Ipamorelin binds the growth hormone secretagogue receptor GHS-R1a on pituitary somatotrophs and on hypothalamic neurons, producing pulsatile growth hormone release ^3,4. This is the ghrelin receptor, not the GHRH receptor, which is the distinction between this family and the GHRH analogues — and it is the basis for the observation that the two classes act synergistically when given together ^1,2.

Selectivity, and why it is the interesting part

The growth hormone-releasing peptides that preceded ipamorelin were not clean. GHRP-6 and GHRP-2 release adrenocorticotropic hormone and cortisol alongside growth hormone, and prolactin as well ^1,2. That matters because a compound intended to raise growth hormone while also raising cortisol is working against itself on body composition, and because chronic cortisol elevation carries its own consequences.

Ipamorelin was engineered to separate these. In the characterisation study, growth hormone release in conscious swine was comparable to GHRP-6, and adrenocorticotropic and prolactin release were not observed ³.

This is the most cleanly demonstrated selectivity claim in Family C, and it is what distinguishes ipamorelin from the compounds it is usually grouped with.

Gastrointestinal motility

The ghrelin receptor is expressed in the enteric nervous system, and ghrelin-receptor stimulation has promotility effects in the upper and lower gastrointestinal tract ⁵. This is a separate pharmacological action from growth hormone release and it is why the compound was taken into postoperative ileus rather than into a body composition indication — the developers pursued the mechanism with the clearest clinical endpoint.

That decision is worth noting: the one indication ipamorelin was formally tested in was not the one it is discussed for.

What has not been established

No human pharmacokinetic profile for subcutaneous ipamorelin appears in the indexed literature. Growth hormone and IGF-1 dose-response curves in humans have not been published for this compound in the way they have for CJC-1295. Urinary metabolites have been characterised after nasal administration alongside the other growth hormone-releasing peptides for anti-doping purposes ⁶, which is disposition data gathered for detection rather than for dosing.

The selectivity was demonstrated in swine. The clinical trial measured gastrointestinal transit. The endocrine effects in humans that the compound is used for sit between those two studies and have not been characterised in either.

04 · Key research findings

The characterisation study. Raun and colleagues established ipamorelin as the first selective growth hormone secretagogue: in conscious swine, growth hormone release with ED50 2.3 ± 0.03 nmol/kg and Emax 65 ± 0.2 ng GH/mL, closely similar to GHRP-6 at ED50 3.9 ± 1.4 nmol/kg and Emax 74 ± 7, with GHRP-2 displaying higher potency — and without the adrenocorticotropic hormone and cortisol release that characterises the other two ³.

A well-executed comparative pharmacology study, and the foundation of everything claimed for this compound.

The clinical trial. A prospective, randomised, controlled, proof-of-concept phase 2 study evaluated ipamorelin for postoperative ileus following abdominal surgery, registered as NCT00672074. Multicentre, double-blind, placebo-controlled, in adults undergoing small and large bowel resection by open or laparoscopic surgery. Intravenous 0.03 mg/kg twice daily from postoperative day 1 to day 7 or discharge. Of 117 patients enrolled, 114 comprised the safety and modified intention-to-treat populations. Overall treatment-emergent adverse events: 87.5% ipamorelin versus 94.8% placebo. Median time to first tolerated meal: 25.3 versus 32.6 hours, p = 0.15. The authors concluded the compound was well tolerated and that no significant differences were seen on the key or secondary efficacy analyses ⁵.

A properly designed trial, adequately reported, with a clear negative result on efficacy and a favourable tolerability comparison.

Class context. Reviews of growth hormone secretagogue safety and efficacy ⁷ and of secretagogue use in body composition management in hypogonadal men ⁸ both include ipamorelin, and recent syntheses in sports medicine, orthopaedics, endocrinology and gerontology list it among compounds with mechanistic rationale and unvalidated clinical outcomes ^{9,10,11,12,13,14,15,16}.

No review identified an efficacy trial beyond the ileus study.

Detection. Urinary metabolites of ipamorelin were characterised alongside GHRP-1, GHRP-2, GHRP-6 and hexarelin following nasal administration to volunteers, for anti-doping method development ⁶.

As with several compounds in this roadmap, the most recent human administration data were generated to catch the compound rather than to evaluate it.

What is absent. No trial of ipamorelin for body composition, muscle mass, recovery from injury, sleep, or ageing was identified in the indexed literature. No human study reporting growth hormone or IGF-1 dose-response for subcutaneous administration was identified.

The uses this compound is discussed for have not been studied.

05 · Evidence overview

06 · Safety profile

Human data. The trial is the safety database, and it is a reasonable one for its size. Treatment-emergent adverse events occurred in 87.5% of the ipamorelin group and 94.8% of the placebo group, in patients recovering from bowel resection — a population in which adverse events are expected at high rates in both arms. The authors concluded that ipamorelin 0.03 mg/kg twice daily for up to seven days was well tolerated ⁵. Nausea and vomiting are indexed among the adverse effects studied in that trial.

Selectivity as a safety property. Not stimulating adrenocorticotropic hormone and cortisol ³ is a safety-relevant property as well as an efficacy one, and it is the clearest argument for preferring ipamorelin to GHRP-6 or GHRP-2 if a ghrelin receptor agonist is being used at all.

Class liability. Growth hormone antagonises insulin action, and glucose tolerance is the principal metabolic consideration for every effective secretagogue ^7,8. No study has characterised this specifically for ipamorelin in humans.

What is genuinely unknown. Exposure beyond seven days — the trial’s maximum ⁵. Any subcutaneous administration data in humans, which is the route used outside clinical research. Growth hormone and IGF-1 response magnitude and duration in humans at any dose. Repeat-dose toxicology, genotoxicity, reproductive and carcinogenicity data, none of which was identified. Immunogenicity of a parenterally administered pentapeptide, unassessed. And whether the selectivity demonstrated in swine ³ holds in humans at the doses used — never directly tested.

07 · US regulatory status

Current as of 6 September 2026. Ipamorelin is not approved as a drug in the United States or any other jurisdiction, and is not a controlled substance.

Ipamorelin acetate appears in FDA’s category 2 bulk drug substances material in two places: in the active category 2 table under the 503B interim policy since 29 September 2023, and in the table of substances nominated but subsequently withdrawn by the nominators ¹⁷. FDA’s stated basis includes immunogenicity risk for certain routes of administration due to aggregation or peptide-related impurities, the presence of unnatural amino acids adding complexity to characterisation, and a published study said to have identified serious adverse events including death when ipamorelin was administered intravenously for improving gastric motility ¹⁷. Ipamorelin was not among the seven substances reviewed by the Pharmacy Compounding Advisory Committee in July 2026 ¹⁸.

A note on that last point. The published trial of intravenous ipamorelin for gastrointestinal motility reports treatment-emergent adverse events in 87.5% of the ipamorelin group against 94.8% of placebo and concludes that the compound was well tolerated ⁵. Its abstract does not report deaths. This guide reports the trial’s own findings and does not assert a mortality signal, because the primary source as published does not describe one. Readers evaluating this compound should read the trial directly.

Under the World Anti-Doping Code, growth hormone secretagogues are prohibited at all times, and urinary detection methods covering ipamorelin have been published ⁶. Competitors should consult the current Prohibited List directly rather than rely on secondary summaries, including this one.

08 · Limitations of the evidence

1. The one controlled trial was negative on efficacy. Median time to first tolerated meal 25.3 versus 32.6 hours, p = 0.15, with no significant differences on key or secondary analyses ⁵. The trial was small and its authors described it as proof-of-concept, so this is not a definitive refutation — but it is the only efficacy evidence that exists.

1. The trial tested an indication nobody uses the compound for. Postoperative ileus after bowel resection is a gastrointestinal motility endpoint. It says nothing about body composition, muscle, recovery or sleep, which is what ipamorelin is discussed for and which no trial has examined.

1. The selectivity claim rests on animal work. The absence of adrenocorticotropic and cortisol release was demonstrated in conscious swine ³ and has not been confirmed in humans at therapeutic doses. It is the compound’s central distinguishing property and it is unverified in the species that matters.

1. No human pharmacokinetics exist for the route used. The trial gave intravenous infusions ⁵; subcutaneous administration has no published human profile. Dose, duration of effect and exposure are therefore unestablished for how the compound is actually administered.

1. No toxicology programme was identified. No repeat-dose, genotoxicity, reproductive or carcinogenicity studies. Seven days is the longest reported human exposure ⁵.

1. Development stopped and the literature does not say why. After a well-conducted 2014 phase 2 study, no further clinical work appears in the indexed record.

1. Regulatory characterisation and the primary source do not clearly agree. The agency rationale references serious adverse events including death from a study of intravenous administration for gastric motility ¹⁷; the trial that matches that description reports the compound as well tolerated with fewer adverse events than placebo ⁵. This guide follows the primary source and flags the discrepancy rather than resolving it.

09 · References

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8. Sinha DK, Balasubramanian A, Tatem AJ, et al. Beyond the androgen receptor: the role of growth hormone secretagogues in the modern management of body composition in hypogonadal males. Transl Androl Urol. 2020;9(Suppl 2):S149–S159.

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14. Dominikowski A, Rękoś Z, Olejarz M, Szczepanek-Parulska E, Domin R, Ruchała M. The emerging landscape of performance-enhancing peptides modulating the GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475.

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16. Mavrych V, Shypilova I, Bolgova O. Therapeutic peptides in gerontology: mechanisms and applications for healthy aging. Front Aging. 2026;7:1790247.

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17. US Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Page current as of 22 April 2026. Regulatory document; no PMID.

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18. US Food and Drug Administration. July 23–24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. Docket FDA-2025-N-6895. Regulatory document; no PMID.

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