Ipamorelin Peptide: Complete Guide to the Selective GH Secretagogue

The claim traces to one set of experiments. In conscious swine, none of the secretagogues tested changed FSH, LH, prolactin or TSH, but GHRP-6 and GHRP-2 both raised ACTH and cortisol. Ipamorelin did not raise ACTH or cortisol beyond the levels seen after GHRH, even at doses more than 200-fold above those needed for half-maximal GH release. On that basis the authors called it the first GHRP-receptor agonist with a GH selectivity similar to GHRH's.^[1]

Why that matters: in healthy men, the older hexapeptide GHRP-6 roughly doubled prolactin and cortisol at its highest tested dose, so the cleaner endocrine profile is a real point of difference within the class. Hexarelin, another GHRP, is compared with ipamorelin in a separate page.^[6]

The limit is equally real. The selectivity data were generated in animals, and the published human pharmacokinetic study of ipamorelin modelled GH responses without reporting ACTH, cortisol or prolactin. A 2026 endocrine review describes the ipamorelin profile as comparatively clean in available human work but places most secretagogues in an evidence tier without controlled efficacy data.^[2][18]

The only published human pharmacokinetic study gave ipamorelin as 15-minute intravenous infusions at five escalating rates to healthy male volunteers, eight per dose level. Exposure rose in proportion to dose, the terminal half-life was about 2 hours, clearance was 0.078 L/h/kg and the volume of distribution at steady state was 0.22 L/kg.^[2]

At every dose the GH response was a single episode, peaking at about 0.67 hours (roughly 40 minutes) and declining exponentially to negligible concentrations. Variability between volunteers was larger for the GH response than for the drug's own kinetics, a reminder that the same exposure does not produce the same pituitary output in everyone.^[2]

Rat data add context. Ipamorelin's systemic clearance was five-fold lower than that of GHRP-6, it was excreted mainly in urine rather than bile, 60-80% was recovered intact, and nasal bioavailability was estimated at about 20%. These are animal figures and should not be read as human values.^[3]

Most of the ipamorelin literature is rodent work. In adult female rats treated for 15 days, it increased longitudinal bone growth in the tibia in a dose-dependent way, from 42 to as much as 52 micrometres per day, together with body-weight gain. Total IGF-1, IGF-binding proteins and bone-turnover markers did not change, and the pituitary GH response to a later challenge was only marginally reduced.^[7]

Over 12 weeks of continuous delivery in young adult female rats, ipamorelin and GHRP-6 increased bone mineral content, but mainly by making bones larger: corrected for the higher body weight, total mineral content was unchanged and volumetric density did not rise. In rats given high-dose glucocorticoids, ipamorelin counteracted the fall in periosteal bone formation and muscle tetanic tension, and it neutralised the steroid-driven negative nitrogen balance, though less efficiently than GH itself at the doses used.^[8][9][10]

These studies establish that ipamorelin behaves like a GH secretagogue in rats. They do not establish any effect in humans: the human studies of GH secretagogues such as ipamorelin did not measure bone, muscle or body-composition endpoints, so recovery and physique claims made for it rest on this animal base.^[18]

One finding rarely appears on product pages. GH itself is lipolytic, yet in mice twice-daily ipamorelin increased fat-pad weights relative to body weight, both in GH-deficient animals and in animals with normal GH. In GH-intact mice, two weeks of ipamorelin or GHRP-6 raised relative body fat measured by DEXA, and the secretagogues, unlike GH, increased serum leptin and food intake. The authors concluded that GH secretagogues can increase body fat through GH-independent mechanisms that may include increased feeding.^[11]

Rat work on post-surgical recovery points the same way: repeated intravenous ipamorelin significantly increased food intake and body-weight gain over 48 hours after abdominal surgery. That is consistent with ipamorelin acting on the ghrelin receptor, whose natural ligand is an appetite signal as well as a GH releaser.^[12][15]

Ipamorelin is often discussed next to MK-677. The differences between the two in chemistry, route and time course are covered in a dedicated comparison rather than repeated here.

Yes, but not for growth, muscle or sleep. Its clinical development targeted post-operative ileus, the stalled gut motility that can follow abdominal surgery. The rationale came from rodents: in rats that had laparotomy with intestinal manipulation, a single intravenous dose shortened the time to first bowel movement, and repeated dosing increased faecal output, food intake and weight gain.^[12]

The human test was a multicentre, double-blind, placebo-controlled phase 2 trial in adults undergoing bowel resection. Of 117 patients enrolled, 114 formed the analysis population; ipamorelin or placebo was infused intravenously twice daily for up to seven days. Median time to the first tolerated solid meal was 25.3 hours with ipamorelin and 32.6 hours with placebo, a difference that was not statistically significant (p = 0.15), and no secondary endpoint differed either. Treatment was well tolerated.^[13]

A larger phase 2 dose-finding study enrolled 320 patients and was completed in 2014, but no results have been posted on its registry record. No ipamorelin product holds an EU marketing authorisation, for this or any other indication.^[14][20]

Not for ipamorelin itself. A PubMed search for 'ipamorelin AND sleep' run on 22 September 2026 returned two review articles and no primary study: no trial, animal or human, has measured sleep with ipamorelin. Sleep claims attached to it are extrapolations.^[16]

The extrapolation starts from ghrelin. In a small study of seven volunteers, intravenous ghrelin given in the late evening increased slow-wave sleep across the night, reduced REM sleep in part of the night and raised GH, prolactin and early-night cortisol. The authors suggested ghrelin may be an endogenous sleep-promoting factor.^[15]

Ipamorelin shares ghrelin's receptor but differs from it in structure, kinetics and, in animals, in its effect on cortisol, so the ghrelin result cannot be transferred to it. Whether ipamorelin changes sleep architecture is an open question. DSIP is compared with ipamorelin on a separate page.^[15][1]

Ipamorelin has no entry in the EMA medicines database and no EU marketing authorisation. The FDA lists ipamorelin acetate in Category 2, bulk substances that may present significant safety risks in compounding, citing possible immunogenicity, the analytical complexity of its unnatural amino acids, and serious adverse events, including death, reported when it was given intravenously in a gastric-motility study. In sport, the WADA 2026 Prohibited List names ipamorelin under S2.2.4, prohibited at all times.^[20][19][21]

Identity is a documented problem in unregulated supply. Anti-doping laboratories analysing black-market products found Gly-ipamorelin, the same peptide with one extra glycine at the N-terminus, confirmed by custom synthesis. A purity percentage alone would not catch that; a certificate of analysis that reports the measured mass would.^[17]

Peptyds supplies ipamorelin as a lyophilised compound with a batch certificate of analysis, for in-vitro laboratory research only. We do not present it as a growth-hormone therapy, a body-composition product or a sleep aid. Researchers comparing it with recombinant GH, or with the CJC-1295 blend it is often paired with, will find both covered in dedicated guides.