Ipamorelin side effects and safety data

What the published trial reported

The 2014 phase 2 trial randomised 117 patients after bowel resection to intravenous ipamorelin 0.03 mg/kg twice daily or placebo, for up to seven days or until discharge [Beck 2014]. Any treatment-emergent adverse event occurred in 87.5% of the ipamorelin group and 94.8% of the placebo group — a high rate in both arms, which is expected in patients recovering from bowel surgery. The authors concluded that ipamorelin was well tolerated.

What FDA reported from the same trial

FDA's 2024 briefing document for the Pharmacy Compounding Advisory Committee reviewed the same publication and set out the detail in a way the abstract does not [FDA briefing 2024]. Its account:

Why the number of patients matters here

Every human safety number on this page comes from 117 patients in a single trial. A trial of that size cannot detect uncommon adverse events at all. A second phase 2 trial randomised 320 patients, listed adverse events as a secondary outcome measure, completed in May 2014 and has never posted results or been published[NCT01280344]. That means roughly three quarters of all patients ever randomised to ipamorelin have safety data that is not in the public record.

Regulatory safety concerns

FDA's Category 2 entry for ipamorelin acetate names four distinct concerns [FDA Category 2]:

• Immunogenicity. The substance may pose a risk for immunogenicity for certain routes of administration, because of the potential for aggregation or peptide-related impurities.
• Characterisation difficulty. Ipamorelin acetate contains unnatural amino acids, which add to the complexity of peptide characterisation — relevant because it makes verifying what is in a given preparation harder.
• The published serious adverse events, as set out above.
• Unknown risk by other routes. FDA states it has not identified safety-related information for certain other injectable routes and lacks sufficient information to know whether the drug would cause harm when given by them.

In October 2024 the Pharmacy Compounding Advisory Committee voted 12 to 0, with one abstention, against adding either ipamorelin form to the 503A Bulks List, recording a lack of information supporting safety and efficacy[PCAC minutes]. The full record is on the regulatory status page.

A separate risk: what is actually in the product

Two analytical studies found that material sold as these peptides was not the peptide named. A 2018 study of black-market growth-promoting products identified Gly-Ipamorelin, carrying an extra N-terminal glycine, and confirmed its identity by custom synthesis [Krug 2018]. A 2019 analysis of preparations seized by Danish customs found glycine-extended analogues of ipamorelin, GHRP-2, GHRP-6 and modified GRF (1-29)[Gajda 2019]. Neither study measured the toxicity of those modified compounds; nothing is known about them. The safety data on this page describes pharmaceutical-grade ipamorelin administered in a hospital, which is not what is being discussed when the subject is purchased material.

Effects measured in animals that have no human counterpart

• Increased food intake and body fat. In mice, ipamorelin increased fat pad weights relative to body weight, relative body fat by DEXA, serum leptin and food intake [Lall 2001].
• Insulin release. Ipamorelin increased insulin secretion from excised pancreatic tissue of both normal and diabetic rats, through calcium channel and adrenergic pathways [Adeghate 2004]. This was tissue in a bath, not a living animal, and no human glucose or insulin endpoint has been measured — though the higher hyperglycemia rate FDA noted in the trial is the nearest human observation.

What is not known

• Any effect of repeated dosing in humans beyond seven days. The trial dosed for up to a week.
• Any human safety data for subcutaneous administration, the route most often discussed outside research.
• Whether immunogenicity actually occurs in humans: it is a stated regulatory concern, not a measurement.
• Anything about long-term use, in any species.
• Any human endocrine safety measurement. ACTH, cortisol and prolactin were measured only in swine[Raun 1998], and the human study measured only growth hormone and ipamorelin concentrations[Gobburu 1999].