Ipamorelin

Five amino acids, one receptor: ipamorelin activates GHS-R1a, the receptor of the stomach hormone ghrelin, which places it in the class of growth hormone secretagogues. The "selective" label dates from the 1998 first description.

What is documented and what is not:

• In pigs, ipamorelin did not push ACTH or cortisol above what the body's own GHRH produces, even at very high doses; GHRP-2 and GHRP-6 did. Prolactin was unchanged with every compound tested. For humans, no published data on these three hormones exist.
• GH was released dose-dependently: demonstrated in rat pituitary cells through a receptor of the GHRP type, and likewise in rats under anaesthesia and in awake pigs.
• A 15-minute infusion into a vein of healthy men generated one GH pulse peaking after roughly 40 minutes; the half-life came to about two hours (Gobburu 1999).
• Ipamorelin is not appetite-neutral: mice gained weight and fat while leptin and food intake rose (Lall 2001); rats recovering from abdominal surgery ate more under repeated dosing (Venkova 2009). A 2026 review rates the effect below that of GHRP-2 and GHRP-6. Human data are absent.

The frequently described pairing with a GHRH analog (typically CJC-1295 lacking DAC) has never been tested in a study. Human evidence of synergy exists only for relatives of ipamorelin combined with native GHRH, and only after one intravenous dose: GHRP-6 in the work of Bowers (1990), ghrelin in that of Arvat (2001).

Exactly two human studies exist: the pharmacokinetics after a single infusion in healthy men and a phase 2 trial involving 114 bowel-resection patients. There, ipamorelin infused twice daily for up to seven days was well tolerated; adverse events occurred in 87.5% versus 94.8% on placebo, and the time to the first solid meal was not significantly shorter. Subcutaneous dosing and longer periods have not been studied in humans, and the cortisol and ACTH selectivity rests on animal data alone.

What applies to the class in general, without specific evidence for ipamorelin: irritation at the injection site, fluid retention, tingling in the hands, higher fasting glucose with temporarily lower insulin sensitivity. Documented in animals: more appetite, more weight, more body fat.

This summary is no substitute for medical advice.

• Ipamorelin, the first selective growth hormone secretagogue - first description with the pig and rat data.
• Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers - infusion study with five dose levels of eight men each.
• Prospective, randomized, controlled, proof-of-concept study of the Ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients - phase 2 trial in 114 patients.