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Peptide Insider

Selective growth hormone secretagogue

Ipamorelin

Also known as NNC 26-0161 · Ipamorelin acetate

Clinical ResearchEARLY CLINICALFDA approved: No

Ipamorelin is a synthetic pentapeptide that activates the ghrelin receptor (GHS-R1a) to stimulate growth hormone release. It was described in 1998 as the first selective growth hormone secretagogue — selective in the sense that, unlike earlier compounds in its class, it raised growth hormone without meaningfully raising ACTH, cortisol or prolactin <Cite id="raun-1998" />. It was subsequently developed not for growth hormone deficiency but for postoperative ileus, on the basis that ghrelin-receptor agonism promotes gastrointestinal motility. That programme produced something rare and valuable in this field: a published, randomised, placebo-controlled Phase 2 trial with a clearly reported result <Cite id="beck-2014" />. The result was negative.

Written by Peptide Insider Editorial TeamPublished Last reviewed

The Insider Summary

What it is
A synthetic pentapeptide ghrelin-receptor agonist that stimulates growth hormone release with comparatively little effect on cortisol, ACTH or prolactin.
Why researchers are interested
Selectivity. Earlier growth hormone secretagogues raised several pituitary hormones at once; ipamorelin was designed and characterised as raising growth hormone in isolation. Its ghrelin-receptor activity also made it a candidate for gastrointestinal motility disorders.
Evidence
Early clinical, and unusually transparent. A randomised, double-blind, placebo-controlled Phase 2 trial in 117 bowel-resection patients did not meet its primary endpoint. The compound was well tolerated.
Regulatory status
Not FDA approved. Ipamorelin acetate is currently listed by FDA in Category 2 of its interim 503A bulk drug substances policy — substances that may present significant safety risks — which is a more restrictive listing than "nomination withdrawn".
Bottom line
Ipamorelin is better characterised than most compounds sold alongside it, and what that characterisation showed was a trial that failed to beat placebo on its primary endpoint. A published negative result is more informative than a shelf of positive animal studies, and it deserves more weight than it usually receives.

Quick reference

Compound
Synthetic peptide agonist
Research areas
Growth Hormone & Endocrine ResearchGastrointestinal Research
Evidence level
EARLY CLINICAL
Research status
Clinical Research
FDA approved
No
Human clinical evidence
Moderate
Sequence
Aib-His-D-2-Nal-D-Phe-Lys-NH2 (pentapeptide)
Last reviewed
17 September 2026

What is ipamorelin?

Ipamorelin is a five-amino-acid synthetic peptide developed in the 1990s at Novo Nordisk as part of a programme searching for growth hormone secretagogues without off-target pituitary effects. The 1998 characterisation paper reported that it released growth hormone comparably to GHRP-6 while leaving ACTH and cortisol essentially unchanged — the property that gave it the "first selective growth hormone secretagogue" description [2].

Its later clinical development went in a different direction. Ghrelin-receptor agonism accelerates gastric emptying and intestinal transit, and postoperative ileus — the temporary shutdown of gut motility after abdominal surgery — is a common, costly and poorly served clinical problem. That indication is where ipamorelin was actually tested in patients.

What is ipamorelin being studied for?

Postoperative ileus. The principal clinical indication. A multicentre, double-blind, placebo-controlled Phase 2 proof-of-concept study randomised 117 patients undergoing bowel resection to intravenous ipamorelin or placebo. Median time to tolerating a standardised solid meal was 25.3 hours with ipamorelin versus 32.6 hours with placebo — a difference that did not reach statistical significance (p = 0.15). The investigators concluded there were no significant differences in the key and secondary efficacy analyses, while noting that ipamorelin was well tolerated [1].

Growth hormone release. Characterised in animal work and in human pharmacokinetic-pharmacodynamic studies. As with other secretagogues, the evidence establishes that hormone concentrations change, not that a clinical outcome improves.

Consumer use. Ipamorelin is widely sold and discussed for body composition and recovery. No published controlled human trials support those uses.

How does Ipamorelin work?

Ipamorelin is an agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a), the receptor for ghrelin. Activation in the pituitary stimulates growth hormone release; activation in the enteric nervous system and stomach is associated with increased gastrointestinal motility, which was the rationale for the postoperative ileus programme. Its defining pharmacological property is selectivity: in the original characterisation it released growth hormone with potency comparable to GHRP-6 but without the accompanying ACTH and cortisol elevation seen with that compound.

Research and clinical evidence

The table below grades the published record separately for each research area, because a compound can be well studied in one context and entirely unstudied in another. Grades follow the Peptide Insider evidence taxonomy.

Evidence level by research area
Research areaEvidence levelWhat the published record shows
Postoperative ileusEARLY CLINICALA randomised, double-blind, placebo-controlled Phase 2 trial in 117 patients did not meet its primary endpoint. Well tolerated.
Growth hormone stimulation (pharmacodynamics)EARLY CLINICALHuman pharmacokinetic-pharmacodynamic work establishes dose-related growth hormone release with selectivity against ACTH, cortisol and prolactin.
Body composition, recovery, anti-ageingINSUFFICIENTNo published controlled human trials identified for these endpoints.

Human clinical studies

Studies conducted in people. These carry the most weight, and their absence is itself a finding.

Randomised, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for postoperative ileus in bowel resection patients[1]

2014
Design
Multicentre, double-blind, placebo-controlled Phase 2; intravenous ipamorelin 0.03 mg/kg or placebo twice daily from postoperative day 1 to day 7 or discharge
Population
Adults undergoing open or laparoscopic small or large bowel resection
Subjects
117 enrolled; 114 in the safety and modified intent-to-treat analyses

FindingsMedian time from first dose to tolerating a standardised solid meal was 25.3 hours with ipamorelin versus 32.6 hours with placebo (p = 0.15). Treatment-emergent adverse events occurred in 87.5% of ipamorelin recipients and 94.8% of placebo recipients. The investigators reported no significant differences in the key and secondary efficacy analyses.

LimitationsA proof-of-concept study, not powered as a definitive efficacy trial. The direction of effect favoured ipamorelin but the difference was not statistically significant, and the trial should be read as failing to demonstrate benefit rather than as demonstrating absence of benefit.

Animal studies

Findings in animal models. Historically, most results at this stage do not reproduce in humans.

Ipamorelin, the first selective growth hormone secretagogue[2]

1998
Design
In vitro and in vivo characterisation in rodent and swine models

FindingsReported growth hormone releasing potency comparable to GHRP-6, without concomitant elevation of ACTH or cortisol — establishing the selectivity that defines the compound.

LimitationsPreclinical characterisation study. Establishes pharmacology, not clinical utility.

FDA and regulatory status

Ipamorelin is not approved by the FDA for any indication.

Its regulatory position differs from several other compounds on this site in an important way. FDA's interim policy page on bulk drug substances that may present significant safety risks lists ipamorelin acetate in Category 2 — substances nominated with sufficient information for evaluation, which may be eligible for the 503A bulks list, but for which FDA has identified significant safety risks [3]. That is a substantive safety determination, not merely an administrative withdrawal of a nomination.

Growth hormone secretagogues are prohibited in competitive sport under World Anti-Doping Agency rules.

Safety and known risks

Risks are separated into what is documented, what is plausible but unestablished, and what has not been studied. The third column is usually the longest one for an unapproved compound, and it is not a reassurance.

Known risks

Documented in regulatory labelling or published trial safety data.

  • In the Phase 2 postoperative ileus trial, treatment-emergent adverse events occurred in 87.5% of ipamorelin recipients versus 94.8% of placebo recipients — a population undergoing bowel surgery, where a high background event rate is expected. The compound was reported as well tolerated.
  • FDA has placed ipamorelin acetate in Category 2 of its interim 503A bulks policy on the basis of identified significant safety risks.

Potential risks

Plausible on mechanism or drug-class grounds, but not established for this compound.

  • Stimulation of the growth hormone axis carries the class-level considerations that appear on approved GH and GHRH-analog labelling: effects on glucose tolerance, fluid retention, joint symptoms, and long-term questions around IGF-1 elevation.
  • Ghrelin receptor agonism affects appetite and gastric motility; sustained activation has not been characterised outside short trials.

Unknown or insufficiently studied

Questions the published record does not currently answer.

  • No published long-term human safety data.
  • No published controlled data on body composition, recovery or ageing-related endpoints.
  • Effects of chronic rather than short-course administration are unstudied.

Frequently asked questions

Did ipamorelin work in human trials?
Not on the endpoint it was tested against. In a randomised, double-blind, placebo-controlled Phase 2 trial of 117 bowel-resection patients, the difference in time to tolerating a solid meal (25.3 vs 32.6 hours) was not statistically significant, and the investigators reported no significant differences across the key and secondary efficacy analyses.[1]
What does “selective” mean for a growth hormone secretagogue?
It means the compound stimulates growth hormone release without also raising other pituitary hormones. Ipamorelin was characterised as releasing growth hormone comparably to GHRP-6 while leaving ACTH and cortisol essentially unchanged.[2]
Is ipamorelin FDA approved?
No. It has no approved indication, and FDA currently lists ipamorelin acetate in Category 2 of its interim 503A bulk drug substances policy — substances for which the agency has identified significant safety risks.[3]
How is ipamorelin different from CJC-1295?
They act on different receptors. Ipamorelin is a ghrelin-receptor (GHS-R1a) agonist; CJC-1295 is a GHRH-receptor agonist. Both raise growth hormone, by different upstream routes, which is why they are frequently discussed together.

Continue reading

Comparison

CJC-1295 vs Ipamorelin

Two growth hormone secretagogues with different receptors and very different evidence. One has Phase 1 hormone data; the other has a published Phase 2 trial that missed its endpoint.

Peptide Science

What Are Peptides?

Peptides are short chains of amino acids. What separates a peptide from a protein, why the body uses them as signals, and why that makes them both useful drugs and difficult ones.

Regulation

Are Peptides FDA Approved?

Some peptides are FDA approved drugs. Most compounds sold as "peptides" are not. Here is how to tell the difference, and what approval does and does not mean.

References

Peptide Insider cites primary sources wherever they exist — regulatory documents, trial registrations and peer-reviewed literature — in preference to secondary summaries.

  1. 1.
    Beck DE, Sweeney WB, McCarter MD, et al.. Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. International Journal of Colorectal Disease, 2014;29(12):1527–1534.
    Peer-reviewedDOI: 10.1007/s00384-014-2030-8
  2. 2.
    Raun K, Hansen BS, Johansen NL, et al.. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology, 1998;139(5):552–561.
    Peer-reviewedPMID: 9849822
  3. 3.
    U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks. FDA, 2026;Page last updated 22 April 2026.
    Regulatory

    Ipamorelin acetate appears in Category 2 on this page.