Overview
Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) and a selective agonist of the ghrelin/growth hormone secretagogue receptor (GHS-R1a). Developed by Novo Nordisk in the late 1990s, it was originally investigated as a potential treatment for postoperative ileus (bowel motility disorders) and has Phase II human trial data in that context. Ipamorelin is distinguished from older GHRPs (GHRP-2, GHRP-6) by its high selectivity — it stimulates GH release with minimal impact on cortisol, ACTH, or prolactin at standard research doses, making it among the most studied GHRPs in the literature.
Mechanism
Ipamorelin acts as a ghrelin mimetic, binding the GHS-R1a receptor on pituitary somatotrophs and hypothalamic neurons to stimulate pulsatile GH release. Unlike GHRH analogs, it works through a distinct pathway — the phospholipase C/IP3 signaling cascade — and is synergistic with GHRH-receptor agonists like CJC-1295 or sermorelin. Its selectivity for GH release over ACTH/cortisol release distinguishes it from less selective GHRPs.
Research Areas
Side Effects (Preclinical)
- – Transient facial flushing
- – Water retention at higher doses
- – Mild headache in some subjects
- – No significant cortisol or prolactin elevation at standard doses
Cautions
- – For research use only — not approved for any therapeutic indication
- – Supraphysiological GH levels carry theoretical risks common to all GH-axis stimulants
Menopause & Women's Health Relevance
Growth hormone secretion declines significantly at menopause alongside estrogen — both hormones decline in tandem and both influence body composition, bone density, and sleep architecture. Ipamorelin's selective GH pulse stimulation (without cortisol elevation) is researched as a way to partially restore GH secretory patterns. Sleep-stage GH release is particularly disrupted by menopausal sleep fragmentation.
What the research shows
Ipamorelin’s selectivity profile is its defining characteristic. Raun et al. (1998) established that it produces GH secretion comparable to GHRP-6 in rat models, but without the cortisol and prolactin elevations seen with GHRP-2 and GHRP-6. This cleaner endocrine profile has made it a preferred research compound when studying isolated GH-axis effects.
The combination of CJC-1295 + ipamorelin is among the most frequently researched GHRH/GHRP pairings due to their complementary receptor targets producing approximately 2–10x greater GH pulse amplitude than either alone.
References
- Ipamorelin, the first selective growth hormone secretagogue — Raun K et al. (1998)
- A phase II study of ipamorelin for prevention of postoperative ileus — Bochicchio G et al. (2011)