Encyclopedia

Ipamorelin is a synthetic pentapeptide and selective agonist of the ghrelin / growth hormone secretagogue receptor (GHS-R). It stimulates pulsatile growth hormone (GH) release from the pituitary and is notably selective — it does not meaningfully raise ACTH, cortisol, or prolactin. It is not FDA-approved, is prohibited in sport, and reached only phase II trials before being discontinued for lack of efficacy in its tested indication.

Ipamorelin (development code NNC 26-0161) was originally developed by Novo Nordisk and is a pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2, derived from the growth-hormone-releasing peptide GHRP-1. It contains non-standard amino acids (aminoisobutyric acid and D-2-naphthylalanine) that improve stability. Its defining pharmacological feature is selectivity: in animal studies it released GH with potency comparable to GHRP-6 but, unlike GHRP-2 and GHRP-6, did not increase ACTH or cortisol. It was investigated in phase II trials for postoperative ileus but discontinued for lack of efficacy. It is widely used non-clinically (often combined with a GHRH analog such as CJC-1295) to stimulate endogenous GH, but has no approved human therapeutic indication.

Mechanism of Action

Selective agonist at the ghrelin/growth hormone secretagogue receptor (GHS-R) on pituitary somatotrophs, stimulating pulsatile GH release. Acts via a GHRP-like receptor pathway distinct from GHRH, and is selective for GH release without significant effect on ACTH, cortisol, prolactin, FSH, LH, or TSH.