Ipamorelin

Ipamorelin has been given to people in two published studies, and neither was looking for the things it is sold for. The first infused it into healthy men to measure how quickly it cleared and how much growth hormone it released. The second gave it or placebo to 114 adults after bowel surgery to see whether their gut recovered sooner. Growth hormone rose in the first. The second did not beat placebo.

Most of the interest traces back to a 1998 animal finding. In pigs, ipamorelin released growth hormone without the ACTH and cortisol rise that GHRP-6 and GHRP-2 produced. That selectivity is real in the species it was measured in. The published volunteer study reports growth hormone only, so whether the same clean profile holds in people is an open question rather than a known one.

It is not FDA approved, WADA names it as a prohibited growth hormone secretagogue, and FDA has published specific safety concerns about compounded ipamorelin acetate.

Ipamorelin is a synthetic pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, described in the European Journal of Endocrinology in 1998 under the title "the first selective growth hormone secretagogue." It came out of a chemistry programme as one of a series of compounds built by removing the central Ala-Trp dipeptide from an older molecule, GHRP-1.

It belongs to the growth hormone releasing peptide family. The surgical trial investigators call it a ghrelin mimetic and a ghrelin-receptor agonist, meaning it acts on the receptor the body's own hunger hormone ghrelin uses. That puts it on a different receptor from sermorelin and tesamorelin, which mimic GHRH and act on the GHRH receptor. Both routes end with the pituitary releasing growth hormone, and they still are not the same signal.

Two Receptors, One Hormone

GHRH works through its own receptor and the protein kinase A pathway. Growth hormone releasing peptides do not bind that receptor. They bind the growth hormone secretagogue receptor, which signals through Gq/i proteins and phospholipase C, and they act at both the pituitary and the hypothalamus. According to the 2018 class review, they do so without disabling the normal negative feedback from somatostatin and IGF-1, so the growth hormone they release comes in pulses rather than a flat rise.

The original pharmacology placed ipamorelin in this family directly. Experiments with GHRP and GHRH antagonists showed it stimulates growth hormone release through a GHRP-like receptor, the same way GHRP-6 does.

What Selective Actually Means

In conscious swine, GHRP-6 and GHRP-2 raised ACTH and cortisol along with growth hormone. Ipamorelin did not raise either above the levels seen after GHRH, even at doses more than 200-fold above its half-maximal dose for growth hormone. None of the peptides tested changed FSH, LH, prolactin or TSH. The authors concluded that ipamorelin was the first GHRP-receptor agonist with a selectivity for growth hormone similar to GHRH itself.

That is a finding about which hormones moved in pigs. It describes a cleaner signal, not a safer drug, and the published volunteer study did not report ACTH, cortisol or prolactin.

How It Behaved in Healthy Men

After a 15-minute intravenous infusion, ipamorelin produced a single episode of growth hormone release that peaked at about 0.67 hours, roughly 40 minutes, then declined exponentially to negligible levels at every dose tested. The peptide had a terminal half-life of about 2 hours, and its kinetics were dose-proportional. The growth hormone response varied more from person to person than blood levels of the drug did.

At this level of evidence, the gap between what was measured and what gets claimed is the whole story.

A growth hormone pulse is a lab value, not a result. The volunteer study recorded growth hormone rising and falling within hours of one infusion. Getting from there to fat loss, muscle, deeper sleep or faster recovery requires steps that have never been measured for ipamorelin in people. Raised growth hormone stays raised growth hormone until a study shows otherwise.

"Selective" was shown in pigs. The clean profile, growth hormone without the ACTH and cortisol rise of GHRP-6 and GHRP-2, comes from swine. The human volunteer abstract reports growth hormone and no other pituitary hormone. A selective signal also says which hormones moved, not whether long-term use is safe.

The only controlled trial missed its endpoint. When ipamorelin went into a randomised, placebo-controlled trial, the question was gut recovery after bowel surgery, and it did not separate from placebo. Pointing to "clinical trials" in support of performance use borrows the phrase without the result.

Class evidence is not compound evidence. A 2018 review of growth hormone secretagogues in humans lists possible effects on appetite, lean mass in wasting states, bone turnover and sleep, drawn from work on GHRP-2, GHRP-6, hexarelin and ibutamoren. Ipamorelin does not appear in that review, and its authors note that few long-term, rigorously controlled studies exist for the class at all.

The controlled human safety data cover up to seven days in hospital. In the bowel surgery trial, treatment-emergent adverse events occurred in 87.5 percent of patients on ipamorelin and 94.8 percent on placebo, and the investigators reported it as well tolerated over that period.

FDA's published concerns about compounded ipamorelin acetate are more pointed. FDA states it may pose a risk of immunogenicity for certain routes because of potential aggregation or peptide-related impurities, and that its unnatural amino acids add to the complexity of characterising the peptide. FDA also states that a published study identified serious adverse events including death when ipamorelin was given intravenously for improving gastric motility, and that it has not identified safety information for certain other injectable routes, so it lacks sufficient information to know whether the drug would cause harm by those routes. The trial abstract above does not report deaths, and the FDA page does not name the study it refers to.

Across the secretagogue class, the 2018 review raises a concern about increases in blood glucose through reduced insulin sensitivity, and says long-term safety, including cancer incidence and mortality, has yet to be evaluated.

What the evidence shows: in healthy men, ipamorelin produces a single, short growth hormone pulse that is gone within hours, and in pigs it does so without pulling ACTH or cortisol up with it. In 114 surgical patients randomised against placebo, adverse event rates were similar between arms over up to a week, and the gut recovery it was being tested for did not improve significantly.

What it does not show: any effect a person taking it would actually feel or see. Body composition, recovery, sleep and ageing were never endpoints. The short-term hormone response is documented. The practical consequences of that response are not.

Anyone describing benefits beyond the growth hormone pulse is describing something these studies did not measure.

Not an approved medicine. FDA has not approved ipamorelin. It left FDA Category 2 on or about 2026-04-22 because the nominators withdrew the nomination, not because FDA resolved its safety concerns, and those concerns remain published. FDA lists it as "Ipamorelin acetate". The 503A nomination was withdrawn, but it remains in Category 2 under section 503B, which governs outsourcing facilities, where it was added 2023-09-29.

Not a GHRH analogue. It acts on the ghrelin, or growth hormone secretagogue, receptor. Sermorelin and tesamorelin act on the GHRH receptor. Grouping them together because all three end in growth hormone release blurs two different signals.

Not permitted in tested sport. WADA prohibits it under class S2.2.4, where it is named among the growth hormone secretagogues.

Not a proven post-surgical treatment either. The one clinical indication it was trialled for, recovery of gut function after bowel resection, did not show a statistically significant benefit over placebo.

I find ipamorelin more interesting as drug design than as something to pursue. Remove a dipeptide from an older molecule and you get growth hormone release in pigs without the cortisol spillover its relatives cause. That is a neat result, and it is fair to say so.

What I will not do is let a hormone pulse in a small group of healthy men stand in for outcomes nobody measured. The one time ipamorelin faced a real placebo-controlled test, it missed its endpoint. That does not make it dangerous or useless. It means the case for it in people has not been made, and I would rather say that plainly than dress a pharmacology paper up as proof of benefit.

I am not going to tell you to use it and I am not going to publish doses. If the human research moves, this page moves with it.