Peptide Evidence Index

Ipamorelin

Evidence last reviewed: September 2026

Quick answers

What is it?: Ipamorelin is a fully synthetic five-amino-acid peptide (a pentapeptide) engineered in a lab to trigger the same receptor as the hunger hormone ghrelin, causing a pulse of growth hormone release.
Why are people interested in it?: People take it hoping for muscle, fat-loss, sleep or anti-aging effects, but its only real human trials tested something else entirely — post-surgical bowel recovery — and neither trial ever released what it found.
What has actually been studied?: Two completed, placebo-controlled Phase 2 hospital trials (117 and 320 patients) testing whether ipamorelin sped bowel-function recovery after abdominal surgery, plus original animal pharmacology in rats and pigs.
How strong is the evidence?: Effectively unknown in humans. Both real trials were sizeable and controlled, but neither has ever published or posted a result, so there is no public evidence of what happened.
What don't we know yet?: What the 320-person surgical trial actually found, whether ipamorelin affects muscle, fat, sleep or aging in healthy adults (never tested), and why two funded Phase 2 trials were never published.
Where can I read the original research?: Sources at the bottom of this page: Raun et al., European Journal of Endocrinology 1998; ClinicalTrials.gov NCT01280344.

Plain-English overview

Ipamorelin is a small, fully synthetic chain of five amino acids, originally designed by Novo Nordisk researchers to act on the growth-hormone-secretagogue receptor — the same docking site targeted by the natural hunger hormone ghrelin — triggering the pituitary gland to release a pulse of growth hormone. Unlike some peptides in this library, it isn't a copy of anything the body already makes. It is not approved as a medicine anywhere and is sold only as an unregulated research chemical. Two real, sizeable human trials exist, both testing recovery of bowel function after abdominal surgery, but neither has ever published or posted its results — the central and most important fact about this compound. No human trial has tested it for muscle growth, fat loss, sleep or anti-aging, the reasons it is most commonly bought today.

What researchers are studying it for

recovery of gut function after bowel surgery
post-operative ileus

Current evidence level

Animal only

Regulatory status: Not an approved medicine. Evidence strength and approval are scored separately; approval is a regulatory decision about a specific use, not a measure of how much research exists.

Human research

Two trials of ipamorelin are registered on ClinicalTrials.gov, both sponsored by Helsinn Therapeutics and both marked complete. The larger, NCT01280344, was a Phase 2 dose-finding trial in 320 adults recovering from small or large bowel resection surgery, completed in 2014, testing whether ipamorelin sped return of gastrointestinal function. The second, NCT00672074, was a Phase 2 trial in 117 patients with post-operative ileus (temporary bowel paralysis after surgery), completed in 2009, testing the same kind of recovery. Both trials used multiple pre-defined injectable dose levels compared against placebo in hospitalized surgical patients. Neither trial has ever posted a summary result, an outcome, or any finding on the registry, and no published journal article describing either trial's results could be located, more than a decade after the larger one finished. That means there is no way, from public information, to know whether a well-powered, 320-person, placebo-controlled human trial of ipamorelin found any benefit at all. Neither trial measured muscle mass, fat loss, sleep, or anti-aging outcomes.

Animal and preclinical research

The original pharmacology, published by Raun and colleagues at Novo Nordisk, showed that ipamorelin reliably released growth hormone from rat pituitary cells in vitro and in live rats and pigs, with potency comparable to another secretagogue, GHRP-6. Notably, even at doses more than 200-fold higher than the amount needed for growth hormone release, ipamorelin did not raise cortisol or ACTH (stress hormones) in pigs, unlike related compounds — a selectivity the original researchers described as distinctive. A later rat study found that ipamorelin, like growth hormone itself, partly offset the nitrogen-wasting effects of steroid treatment on the liver, though less efficiently than growth hormone. Separate rodent work found that ipamorelin's effect on gut motility depends partly on an intact gastrointestinal tract, consistent with a role for the ghrelin receptor.

Major findings

In the original laboratory pharmacology, ipamorelin reliably triggered growth hormone release from rat pituitary cells and in live rats and pigs.
Unlike related secretagogues, ipamorelin did not meaningfully raise cortisol or ACTH (stress hormones) even at very high doses in pigs — a distinguishing, selective animal finding.
Two real Phase 2 human trials were completed — 117 and 320 patients — testing bowel-function recovery after surgery, not muscle, fat, sleep or aging.
Neither completed human trial has ever posted or published its results, despite the larger one finishing over a decade ago.
No published human study of ipamorelin for muscle growth, fat loss, sleep, or anti-aging exists at all.
In rats, ipamorelin partly offset steroid-induced nitrogen wasting in the liver, similar to growth hormone itself, though less efficiently.

What has not been established

What the 320-person surgical-recovery trial actually found — the single biggest unanswered question about this compound.
Whether ipamorelin's selective, low-cortisol effect seen in animals holds true with repeated use in people.
Whether it has any effect on muscle mass, fat loss, sleep, or aging in healthy adults — this has never been tested in a human trial.
Why two completed, well-funded Phase 2 trials were never published or posted.
What long-term pituitary or hormonal effects repeated use might have.

Important limitations

The two real human trials that exist were never published, so nothing about their actual findings can be verified or cited.
No human trial has tested the uses ipamorelin is marketed for today (muscle, fat, sleep, anti-aging) — only post-surgical bowel recovery.
The animal pharmacology is decades old and was conducted by the compound's own commercial developer, Novo Nordisk.
Doses circulating online for non-surgical uses trace to animal-to-human weight conversions never tested for safety or effect in people.

Regulatory status

Ipamorelin is not approved as a medicine anywhere and is sold only as an unregulated research chemical.

Primary research sources

Raun K, Hansen BS, Johansen NL, et al., "Ipamorelin, the first selective growth hormone secretagogue": European Journal of Endocrinology 1998; PMID 9849822, DOI 10.1530/eje.0.1390552
Ipamorelin for recovery of gastrointestinal function after bowel resection: ClinicalTrials.gov NCT01280344, n=320, Phase 2, Helsinn Therapeutics, completed 2014, no results posted
Ipamorelin for management of post-operative ileus: ClinicalTrials.gov NCT00672074, n=117, Phase 2, Helsinn Therapeutics, completed 2009, no results posted
Venkova K, Mann W, Nelson R, Greenwood-Van Meerveld B, "Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus": Journal of Pharmacology and Experimental Therapeutics 2009; PMID 19289567, DOI 10.1124/jpet.108.149211
Aagaard NK, Grøfte T, Greisen J, et al., "Growth hormone and growth hormone secretagogue effects on nitrogen balance and urea synthesis in steroid treated rats": Growth Hormone & IGF Research 2009; PMID 19231263, DOI 10.1016/j.ghir.2009.01.001
Tewari K, Liu TP, Im C, et al., "Peptide Supplements and Their Therapeutic Applications in Sports Medicine" (scoping review covering ipamorelin, CJC-1295, BPC-157 and others): American Journal of Sports Medicine 2026; PMID 42578445, DOI 10.1177/03635465261464420

Full evidence entry (complete data, registry records, dosing evidence)

Animal only

Studied in animals; human evidence absent or minimal

At a glance

Also known as: Ipamorelin acetate
Class: Synthetic pentapeptide, growth hormone secretagogue
Derived from: A lab-designed pentapeptide, not derived from a natural human hormone, engineered to selectively trigger the ghrelin / growth-hormone-secretagogue receptor
Registered human trials: 2
…with published results: 0
Largest human trial: 320 adults recovering from bowel resection surgery (Phase 2, Helsinn Therapeutics, completed 2014) — testing recovery of gut function after surgery, not muscle growth or anti-aging. No results have ever been posted or published.
Studied for: recovery of gut function after bowel surgery, post-operative ileus
Dosing evidence: Doses used in trialsMultiple dose levels of injectable ipamorelin were used in two completed hospital-based surgical-recovery trials, but neither trial ever disclosed what those doses did — so there is no way to know if any of them worked.
Regulatory status: Not approved as a medicine anywhere.

What it is

Ipamorelin is a small, entirely synthetic chain of five amino acids (a pentapeptide). Unlike some other peptides in this library, it isn't a modified copy of something the body already makes — it was designed in a laboratory, originally by Novo Nordisk researchers, to act on a specific docking site in the body, the growth-hormone-secretagogue receptor, the same receptor targeted by the natural hunger hormone ghrelin. Triggering that receptor causes the pituitary gland to release a pulse of growth hormone.

It is not approved as a medicine anywhere and is sold only as an unregulated research chemical.

What the studies actually found

In animals — rats and pigs, in the original laboratory studies — ipamorelin reliably triggered a release of growth hormone. Notably, those animal studies also found that, unlike some related compounds, it did not meaningfully raise cortisol or ACTH (stress hormones), suggesting a more selective action. That is a real and specific animal finding.

In humans, two hospital-based trials were run, both testing whether ipamorelin could speed the return of normal bowel function after abdominal surgery — a real medical problem for surgical patients. Both trials were completed years ago. Neither has ever published or posted what happened.

What exists in humans

Two trials are registered on ClinicalTrials.gov, both sponsored by Helsinn Therapeutics and both completed:

A Phase 2 dose-finding trial in 320 patients recovering from small or large bowel resection surgery,

completed in 2014, testing whether ipamorelin sped the recovery of gastrointestinal function.

A Phase 2 trial in 117 patients with post-operative ileus (temporary bowel paralysis after surgery),

completed in 2009, testing the same kind of recovery.

Both trials are marked complete on the registry. Neither has posted results — not a summary, not an outcome, nothing — more than a decade after the larger trial finished. No published journal article describing what either trial found could be located either.

This is the single most important fact about ipamorelin: a pharmaceutical company ran a real, 320-person, controlled hospital trial, and the outcome was never made public. That's different from a trial that's still running, or one that found nothing interesting and simply wasn't written up — there is no way, from public information, to know what a well-powered human trial of this compound found.

Neither trial studied muscle growth, fat loss, sleep, or anti-aging — the uses ipamorelin is most commonly marketed for today.

What doses have been studied in humans

Both completed trials used multiple, pre-defined injectable dose levels of ipamorelin compared against a placebo, given to hospitalized surgical patients over the days immediately following their operation. Because neither trial ever reported which dose, if any, helped recovery, there is no dose of ipamorelin that human research has shown to work — for that purpose, or for any other purpose.

No trial has tested ipamorelin in healthy adults for muscle, fat, sleep, or anti-aging outcomes, the reasons it is most often bought today. Amounts described online for those uses do not come from any published or disclosed human study, and typically trace to animal dosing scaled to human weight — a conversion that estimates comparable exposure, not effectiveness or safety.

What remains unknown

What the 320-person surgical-recovery trial actually found — the central unanswered question
Whether ipamorelin's selective, low-cortisol effect seen in animals holds true with repeated use in people
Whether it has any effect on muscle mass, fat loss, sleep, or aging in healthy adults — this has never been tested
Why two completed, well-funded Phase 2 trials were never published
What long-term pituitary or hormonal effects repeated use might have
What is actually in an unregulated vial sold as "ipamorelin" online

Registry and study records

Ipamorelin, the first selective growth hormone secretagogue: PubMed · DOI: 10.1530/eje.0.1390552 — original animal pharmacology (rats, pigs), Novo Nordisk
Ipamorelin for recovery of gastrointestinal function after bowel resection: ClinicalTrials.gov NCT01280344 · n=320, Phase 2, Helsinn Therapeutics, completed 2014, no results posted
Ipamorelin for management of post-operative ileus: ClinicalTrials.gov NCT00672074 · n=117, Phase 2, Helsinn Therapeutics, completed 2009, no results posted

See the full Evidence Index →

Evidence last reviewed: September 2026. Peptide Proof reports what studies found. We do not give medical advice, dosing guidance, or treatment recommendations.