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Why this evidence grade
Human trials
Phase 1 pharmacology in volunteers and one phase 2 trial in post-surgical ileus that did not meet its primary endpoint. Nothing on muscle, fat or anti-aging.
What it is
Ipamorelin is a synthetic pentapeptide that activates the ghrelin (growth hormone secretagogue) receptor. It was developed as a selective GH-releasing agent and was tested for post-operative ileus, but is not approved for any use.
How it is thought to work
It binds the ghrelin receptor in the pituitary, causing a short pulse of growth hormone release. In volunteers the pulse peaked around 40 minutes after infusion and faded to baseline.
What the studies found6 studies explained
A dose-escalation study in 40 healthy men characterised its pharmacokinetics (half-life about 2 hours) and GH response. A randomized phase 2 trial in 117 patients with post-operative ileus found a numerically shorter time to first tolerated meal (25.3 vs 32.6 hours) that was not statistically significant. A second, larger phase 2 post-surgery trial (NCT01280344, 320 patients) is registered as completed, but no results were posted on ClinicalTrials.gov when we checked. Rat studies suggest effects on bone growth.
animalPreclinical pharmacology (cells, rats and pigs)
Who / how many
Rat pituitary cells, anaesthetized rats and conscious swine
What they found
Ipamorelin released growth hormone with potency and efficacy comparable to GHRP-6 through a GHRP-like receptor, and unlike some other secretagogues did not raise ACTH or cortisol, even at much higher doses.
Limitations
Developer's early pharmacology paper in animals and cells. Selectivity in animals may not carry over to long-term use in people.
Johansen PB, Nowak J, Skjaerbaek C · Growth Horm IGF Res · 1999 · PMID 10373343
animalControlled animal experiment
Who / how many
Adult female rats given ipamorelin three times daily for 15 days
What they found
Ipamorelin dose-dependently increased the rate of longitudinal bone growth (42 to 52 microm/day) and body weight gain, without changing IGF-I or bone turnover markers.
Limitations
Short rat study. The authors say clinical studies would be needed to know whether it helps children with growth problems.
Venkova K, Mann W, Nelson R · J Pharmacol Exp Ther · 2009 · PMID 19289567
animalControlled animal experiment
Who / how many
Rats after abdominal surgery
What they found
Repeated intravenous ipamorelin increased fecal pellet output, food intake and weight gain, and a single dose shortened the time to the first bowel movement.
Limitations
Rodent model that led to the human ileus trial, which later missed its primary endpoint.
Adult female rats given methylprednisolone with or without ipamorelin for 3 months
What they found
Ipamorelin counteracted glucocorticoid-induced loss of muscle strength and bone formation (periosteal bone formation rate was four times higher than with the steroid alone).
Limitations
Rat model of steroid-induced muscle and bone loss, not healthy muscle gain, and not tested in people.
2 trials on ClinicalTrials.gov list Ipamorelin as an intervention; the most advanced are shown. Registration is not evidence of benefit: many trials are ongoing, unpublished or never reported results.
Data pulled from the ClinicalTrials.gov API. Check sponsors: several newer peptide registrations come from companies that also sell the product.
European research
49 records in Europe PMC mention Ipamorelin in the title or abstract. Of the 25 most-cited with European author affiliations that we sampled, the most common countries were Denmark (12), Germany (7), Switzerland (2), United Kingdom (1).
In the ileus trial adverse events were common in both groups (87.5% ipamorelin vs 94.8% placebo), largely reflecting surgery. Long-term safety of repeated use for muscle or "anti-aging" has not been studied in controlled trials.
Legal status
United States
Not FDA-approved. Compounding status uncertain; verify with the FDA 503A bulks list.
Canada
Not an authorized drug in Canada.
European Union
No EU marketing authorization from the EMA.
Sport (WADA)
Prohibited at all times in sport (growth hormone secretagogues, S2).
Last verified . Rules for this substance are changing; check the sources below. WADA Prohibited List.
Common questions
Has ipamorelin been tested in humans?
Yes, in a volunteer pharmacology study and a phase 2 post-surgery trial, but not for muscle gain, fat loss or anti-aging.
