Ipamorelin

Ipamorelin is a selective pentapeptide that acts as an agonist at the growth hormone secretagogue receptor (GHS-R1a), also known as the ghrelin receptor, located on somatotroph cells of the anterior pituitary. By mimicking the endogenous hunger hormone ghrelin at this receptor, it triggers a targeted pulse of growth hormone release.

What makes Ipamorelin exceptional among GH secretagogues is its remarkable selectivity. Unlike GHRP-6, GHRP-2, and hexarelin — which also stimulate cortisol, prolactin, and ACTH release — Ipamorelin produces a clean GH pulse with minimal impact on other hormonal axes. This selectivity is attributed to its unique non-peptide backbone modifications that confer high receptor specificity.

The GH pulses stimulated by Ipamorelin follow a dose-dependent, saturable pattern that closely mimics physiological GH secretion. This means higher doses produce proportionally larger GH responses up to a ceiling, after which additional peptide has no further effect — a safety feature that prevents supraphysiological GH spikes.

Ipamorelin was first described in 1998 by researchers at Novo Nordisk as part of a programme to develop selective GH secretagogues with fewer side effects than existing compounds. The initial characterisation demonstrated its remarkable selectivity — releasing GH without affecting cortisol, prolactin, FSH, LH, or TSH levels.

Subsequent research throughout the 2000s and 2010s expanded the understanding of Ipamorelin's applications. Studies investigated its effects on bone density, body composition, gut motility (it became the first GHS-R agonist tested for post-operative ileus), and sleep quality. Its favourable side-effect profile has made it one of the most popular GH peptides in research settings, and it is frequently studied in combination with GHRH analogues like CJC-1295.