Ipamorelin

Overview

Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) originally developed by Novo Nordisk and later advanced by Helsinn/Nycomed. It is a selective ghrelin receptor agonist / growth hormone secretagogue (GHRP). Its defining feature versus older GHRPs (GHRP-2, GHRP-6, hexarelin) is that in preclinical and early clinical studies it raised GH without meaningfully increasing ACTH, cortisol, or prolactin. It is not FDA-approved for any indication; a Phase 2 trial for postoperative ileus failed to meet its primary endpoint and clinical development was discontinued. In the wellness/grey market it is sold as a research chemical and used off-label for anti-aging and body-composition goals despite no clinically validated human dose for those uses.

Mechanism of Action

Ipamorelin binds the growth hormone secretagogue receptor 1a (GHSR-1a) on pituitary somatotrophs and in the arcuate nucleus of the hypothalamus, mimicking endogenous ghrelin. GHSR-1a is a Gq-coupled GPCR; activation triggers phospholipase C, IP3, and intracellular calcium release, driving pulsatile GH secretion. Ipamorelin's selectivity appears to come from its distinct binding profile at the GHSR compared with GHRP-2/GHRP-6, producing GH release without substantial ACTH/cortisol or prolactin co-release at therapeutic doses. It is pharmacologically complementary to GHRH analogs (sermorelin, CJC-1295) because the two receptor systems converge on somatotroph GH release through different second messengers, producing additive-to-synergistic GH pulses when co-administered.

Research Summary

The seminal preclinical characterization (Raun et al., 1998) established ipamorelin as the first GHRP-receptor agonist with a GH-release selectivity comparable to GHRH, without raising ACTH or cortisol even at doses more than 200-fold above the ED50 for GH. Pharmacokinetic-pharmacodynamic modeling in healthy male volunteers (Gobburu et al., 1999) confirmed a roughly 2-hour half-life and dose-dependent GH response following IV infusion. The most advanced human study is Beck et al. (2014), a Phase 2, randomized, double-blind, placebo-controlled trial in 114 patients after bowel resection evaluating IV ipamorelin 0.03 mg/kg twice daily for postoperative ileus; the drug was well tolerated but did not separate from placebo on the primary endpoint (time to tolerance of solid food), and the sponsor discontinued development. There are no completed registrational trials in adult growth hormone deficiency, frailty, or body-composition indications. Use in wellness medicine for anti-aging, fat loss, or muscle gain is extrapolated from short-term GH/IGF-1 pharmacodynamic data and is not clinically validated.

Dosing Information

Reported Side Effects

• Injection-site reactions (erythema, itching, transient welt)
• Transient mild water retention / peripheral edema
• Increased appetite (ghrelin-class effect)
• Headache and flushing shortly after injection
• Paresthesias (tingling or numbness in hands or feet)
• Transient post-dose fatigue or lightheadedness
• Reduced insulin sensitivity / elevated fasting glucose with sustained GH elevation, of particular concern when stacked with long-acting GHRH analogs in predisposed individuals

Research References

• Ipamorelin, the first selective growth hormone secretagogue (Raun K et al., Eur J Endocrinol, 1998) (1998)
• Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers (Gobburu JV et al., Pharm Res, 1999) (1999)
• Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients (Beck DE et al., Int J Colorectal Dis, 2014) (2014)