Ipamorelin is a small peptide that prompts the pituitary to release growth hormone. Research asks how cleanly it can do that.
Ipamorelin · Ghrelin-receptor GH secretagogue
Growth hormone is released by the pituitary in pulses, on instruction from the brain and the gut. One of those instructions is ghrelin, better known as a hunger signal, which also acts on pituitary cells. Ipamorelin was designed to mimic that instruction. Researchers use it to test whether growth hormone release can be triggered without also raising stress hormones. The evidence is from animals and small human studies.
Ipamorelin is a synthetic pentapeptide, five amino acids, with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2; several of the residues are non-natural, chosen to resist breakdown. It is a growth hormone secretagogue, a molecule that causes the release of growth hormone (GH), and it acts as an agonist at the ghrelin receptor: it activates the same cellular receiver that ghrelin uses.
That places it in a different category from GH itself and from GHRH analogues such as CJC-1295 or tesamorelin. GHRH is the hypothalamic hormone that releases GH through its own receptor; ghrelin-receptor agonists prompt release through a second, separate route. Ipamorelin was characterised at Novo Nordisk in the 1990s by Raun and colleagues (1998), who described it as the first ghrelin-receptor agonist with selectivity for GH release comparable to GHRH's.
The selectivity claim is specific to the models used. Raun and colleagues measured GH release in cultured rat pituitary cells, in anaesthetised rats and in conscious pigs. In the pigs, earlier peptides GHRP-6 and GHRP-2 raised ACTH and cortisol alongside GH, whereas ipamorelin did not, even at doses more than 200 times its effective GH dose; none of the compounds changed prolactin, thyroid-stimulating hormone or the gonadotrophins. Whether the same profile holds in people was not tested in that paper.
In healthy men, Gobburu and colleagues (1999) gave escalating intravenous infusions and measured a single GH pulse peaking at about 40 minutes, with a plasma half-life of around two hours. That study measured GH and drug levels, not body composition or any clinical outcome.
The one randomised clinical trial identified used a different rationale: ghrelin-receptor stimulation also moves the gut. Beck and colleagues (2014) tested intravenous ipamorelin against placebo in 114 patients recovering from bowel surgery and found no significant difference in time to tolerating a solid meal. Ipamorelin has not been approved as a medicine in any jurisdiction identified for this note. Reviews of secretagogues in body-composition contexts, such as Sinha and colleagues (2020), describe the clinical data as largely lacking.
Selectivity shown in pigs and rats is a property of those experiments; the hormonal profile of repeated administration in humans has not been characterised. A GH pulse in a volunteer study does not show downstream effects on muscle, fat or metabolism over time, which have not been measured for ipamorelin in a controlled trial. No published study of ipamorelin combined with a GHRH analogue was identified for this note, so claims about such combinations rest on reasoning about separate receptors, not on evidence. Safety with long-term use in people is unknown.
In Australia ipamorelin is a Schedule 4 (prescription only) substance under the Poisons Standard (June 2026), and listed in Appendix D (clause 5), which the states and territories apply through their own poisons legislation to restrict possession without authority; growth hormone secretagogues are also scheduled as a class. It is not an approved medicine in Australia, and no approval elsewhere was identified. Ipamorelin is named under S2.2.4 on the WADA 2026 Prohibited List, prohibited at all times.
Sources and status checked 2026-09-22
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