Ipamorelin

Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) classified as a growth hormone secretagogue and an agonist of the growth hormone secretagogue receptor, better known as the ghrelin receptor. It was developed at Novo Nordisk in the 1990s out of a medicinal-chemistry program on growth hormone-releasing peptides (GHRPs) and was described as the first GHRP-receptor agonist whose selectivity for GH release rivals that of growth hormone-releasing hormone itself ^[1].

The defining property that distinguishes ipamorelin from earlier secretagogues such as GHRP-6 and GHRP-2 is its specificity. In animal studies it released growth hormone with potency and efficacy comparable to GHRP-6, yet, unlike those peptides, it did not stimulate the release of adrenocorticotropic hormone (ACTH) or cortisol, and it left luteinizing hormone, follicle-stimulating hormone, prolactin, and thyroid-stimulating hormone unaffected ^[1]. This clean, GH-selective signature is the central reason it drew interest for potential clinical development. Its GH-releasing action is mediated through the same ghrelin-receptor pathway targeted by the stomach hormone ghrelin, and the peptide is used as a reference ligand in efforts to image that receptor ^[4][5].

Beyond growth hormone, ipamorelin has been studied for effects that follow from ghrelin-receptor activation. It counteracted steroid-induced catabolism in rats, improving nitrogen balance and reducing hepatic nitrogen wasting during prednisolone treatment ^[3], and, as a ghrelin mimetic, it accelerated gastrointestinal transit and improved recovery in a rodent model of postoperative ileus, increasing food intake and body weight with repeated dosing ^[2]. Ipamorelin is not an approved medicine; it is handled as a research peptide.

As a growth hormone secretagogue, ipamorelin raises GH and downstream IGF-1, which can cause fluid retention, joint or muscle aches, tingling in the extremities, and headache. Sustained elevation of these hormones may impair glucose tolerance and promote insulin resistance, and long-term human safety has not been established. It is not an approved medicine, and injectable use carries the usual risks of injection-site reactions and contamination.

Ipamorelin was developed by scientists at the Danish pharmaceutical company Novo Nordisk and first described in a landmark 1998 paper by Kurt Raun and colleagues, which introduced it as "the first selective growth hormone secretagogue." It emerged from a medicinal-chemistry program that removed the central Ala-Trp dipeptide of growth hormone-releasing peptide-1 (GHRP-1), yielding the pentapeptide Aib-His-D-2-Nal-D-Phe-Lys-NH2. In laboratory and animal testing it released growth hormone as potently as earlier GHRPs but, unlike them, did so without raising ACTH or cortisol, establishing its defining selectivity. Although it was investigated for clinical development, ipamorelin was not brought to market as an approved drug and is used today as a research peptide.

Ipamorelin is widely regarded as one of the cleanest and most desirable peptides in the growth hormone secretagogue class, valued precisely for its selectivity. Researchers and users appreciate that it prompts a natural, pulsatile release of growth hormone while sparing the cortisol and prolactin spikes that made older peptides less attractive. This clean hormonal profile, together with documented effects on metabolism and gastrointestinal motility, has made it a benchmark reference compound for the field. As with related peptides, its use in humans remains investigational and outside approved medical indications.