Ipamorelin

A synthetic ghrelin mimic derived from GHRP-1 by removing two central amino acids. It was described as 'the first selective growth hormone secretagogue' by Raun and colleagues in 1998.

It binds the ghrelin receptor on pituitary and hypothalamic cells, triggering a single burst of growth hormone release. In pigs and rats it did not raise ACTH or cortisol, unlike GHRP-2 and GHRP-6, which is the source of its 'selective' label. The ghrelin receptor also speeds gut movement.

In healthy men, IV infusions each produced one growth hormone pulse peaking at about 40 minutes, with a half-life of about 2 hours. A phase 2 trial in 114 bowel-surgery patients found no significant benefit over placebo for gut recovery, and development stopped. In animals it increased bone growth, offset steroid-induced muscle wasting and improved gut motility. FDA found no human data confirming the claimed lack of cortisol or prolactin effects, and no data on repeated use, IGF-1 or body composition.

In the surgical trial, low potassium (12.5% vs 3.4%), insomnia and high blood sugar at discharge (14.3% vs 8.6%) were more common than on placebo. Two patients died after surgical leaks; FDA called the link unclear but listed it as a safety concern. FDA also cites immunogenicity concerns and says risks on growth hormone labels may apply.

Not approved in the US or elsewhere. FDA advisers voted 0–12–1 against adding it to the 503A bulks list in October 2024, and it remains in 503B Category 2 (significant safety risk), so it is not compoundable from bulk powder. WADA prohibits it at all times under S2.4. Status as of October 2026.