What is ipamorelin?

What it is, and what it acts on

The paper that introduced it in 1998 called it the first selective growth hormone secretagogue, and it earned the word selective by testing what else moved. The receptor came first:

GHRP-6 is an older peptide of the same family, so that sentence places ipamorelin outside the GHRH route entirely. A later pharmacology paper names the target plainly, calling it “ipamorelin, a selective growth hormone secretagogue and agonist of the ghrelin receptor”.¹ That is the ghrelin receptor, the one the hunger hormone binds, and it is why ipamorelin belongs to a different class from sermorelin and tesamorelin. The two routes to the same hormone sets them side by side.

The selectivity claim rests on what stayed still. In the same experiments the two comparator peptides raised stress hormones — “Administration of both GHRP-6 and GHRP-2 resulted in increased plasma levels of ACTH and cortisol.”⁴ — while ipamorelin did not, and none of the peptides tested moved the other pituitary hormones at all.⁴ Two things bound that result. It was measured in pigs “The specificity for GH release was studied in swine.”,⁴ and the cortisol finding is a comparison rather than a flat zero, which the cortisol question takes apart sentence by sentence.

In people the wording is softer. A 2026 review of this whole class describes ipamorelin as a synthetic secretagogue acting at GHSR-1a with “Ipamorelin is a synthetic GH secretagogue that acts as a relatively selective agonist of the GHSR-1a receptor, stimulating endogenous GH release while producing comparatively minimal activation of other pituitary–adrenal axes in available human studies”.² Comparatively minimal in humans and does not raise it in pigs are different claims, and this site prints both rather than picking the stronger one.

What it's used for

Nothing, officially. The review above puts ipamorelin among the compounds where, with one exception that is not this one, “With the singular exception of tesamorelin within its approved HIV-lipodystrophy indication, none of these compounds carry regulatory approval for performance- or appearance-related use”.² The exception is tesamorelin inside its HIV indication, which is a different molecule with its own label.

It did have a clinical program, and it was not about muscle or aging. A drug company took it into surgery, for the gut stall that follows a bowel operation:

That trial enrolled 117 patients, of whom 114 formed its safety and analysis populations,³ and it did not find what it was looking for: “There were no significant differences between ipamorelin and placebo in the key and secondary efficacy analyses.”³ The 2026 review reads the same result as the end of the road, saying the findings “results from a randomized, controlled proof-of-concept clinical study in patients undergoing bowel resection did not show a statistically significant improvement in postoperative gastrointestinal recovery compared with placebo” and tempered further investigation in that setting.² What the trial did record about side effects is on ipamorelin side effects.

What people actually buy it for is a separate question with a separate kind of evidence behind it. The same review sets the bodybuilding-forum use out in a table it labels “anthropological/behavioural data, not clinical recommendations”,² and the pairing with CJC-1295 that most sellers list is described there as driven by anecdotal rationale rather than controlled evidence.² Whether you can buy it by itself at all is answered on can you buy ipamorelin on its own.

How long it lasts

One paper reports it, and it reports the design alongside the figure: “A trial was conducted with a dose escalation design comprising 5 different infusion rates (4.21, 14.02, 42.13, 84.27 and 140.45 nmol/kg over 15 minutes) with eight healthy male subjects at each dose level.”⁵ Out of that came the number this site records — “The PK parameters showed dose-proportionality, with a short terminal half-life of 2 hours”.⁵

The growth hormone it sets off comes and goes faster than the peptide does. The same paper describes “The time course of GH stimulation by ipamorelin showed a single episode of GH release with a peak at 0.67 hours and an exponential decline to negligible GH concentration at all doses.”⁵ — one rise, peaking about forty minutes in, then back down. A review of the class puts the peak in healthy adults in the same place, reporting a clear response “In a phase I study in healthy adults, ipamorelin was generally well tolerated and produced a clear GH response, with peak GH levels occurring approximately 40–60 minutes after administration; importantly, no significant effects on other pituitary or adrenal hormones were reported in that setting”.²

So the honest description is a short push on a hormone the body releases in pulses anyway, not a level held up over a day. The half-life calculator runs the arithmetic for any interval, and the axis on the home page puts every recorded figure on one scale, which is the fastest way to see how far apart these five molecules sit.

Which route has actually been studied

Both human studies used a vein. The pharmacokinetic work was infusions,⁵ and the surgical trial was intravenous too, given twice a day in hospital to “The patients were adults undergoing small and large bowel resection by open or laparoscopic surgery.”³ That matters for anyone reading a figure off this page, because a rate measured in an infusion is not automatically the rate under skin.

The FDA has said the same thing from the other direction. Its compounding page records that the agency “FDA has not identified safety-related information regarding ipamorelin acetate via certain other injectable routes of administration. Therefore, the agency lacks sufficient information to know whether the drug would cause harm if administered to humans via those routes.”⁶

The same regulatory page gives two reasons it is on the list at all, both about the substance rather than the route: compounded drugs containing it “Compounded drugs containing Ipamorelin acetate may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation or peptide-related impurities.” and it “Ipamorelin acetate also contains unnatural amino acids, which add to the complexity of peptide characterization.”⁶ Category 2 is defined on the page itself: “Bulk drug substances that may present significant safety risks have been placed in category 2 under the interim policies.”⁶ The page was read in September 2026.

Questions that come next

Sources