Ipamorelin

Ipamorelin is a synthetic pentapeptide (sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2) originally developed by Novo Nordisk under the code NNC 26-0161 and first described by Raun and colleagues in 1998. It belongs to the growth hormone secretagogue (GHS) / growth hormone-releasing peptide (GHRP) family and was the first compound in its class described as a truly selective GH secretagogue. It is an investigational compound that never reached marketing approval; today it circulates largely as a research chemical and within some compounding-pharmacy and wellness channels.

Education only. This page summarises published research and regulatory status. It is not medical advice and gives no dosing, preparation or administration instructions; any decision about use belongs with an independent qualified professional.

Also known as

NNC 26-0161, NNC26-0161, Aib-His-D-2-Nal-D-Phe-Lys-NH2

Class

Growth hormone secretagogue (selective ghrelin / GHS-R1a receptor agonist); synthetic pentapeptide

How does Ipamorelin work?

Ipamorelin binds and activates the ghrelin receptor (growth hormone secretagogue receptor, GHS-R1a), a G-protein-coupled receptor on pituitary somatotrophs and in the hypothalamus. Activation triggers intracellular signaling that stimulates a pulse of growth hormone (GH) release, which in turn can raise downstream IGF-1. Unlike the endogenous ligand ghrelin and several other GHRPs (such as GHRP-6), at therapeutic doses ipamorelin releases GH without meaningfully elevating ACTH, cortisol, or prolactin, and it tends to preserve the body's natural pulsatile pattern of GH secretion rather than forcing continuous elevation. This selectivity is the property that distinguished it within its class.

What has Ipamorelin been studied for?

• Stimulation of growth hormone release (pituitary GH secretagogue activity) in animal and early human studies
• Bone mineral content / bone formation in rodent models, including counteracting glucocorticoid-induced reductions in bone formation
• Treatment of postoperative ileus / restoration of gastrointestinal motility (Phase II clinical trials)
• Body composition and growth effects in preclinical models

What does the evidence show?

Evidence is limited and mostly preclinical. The foundational pharmacology (selective GH release without cortisol/prolactin elevation; bone effects) comes from rodent studies in the late 1990s and early 2000s (Raun et al. 1998; Svensson et al. and related bone work). Human data is sparse: a dose-escalation pharmacokinetic-pharmacodynamic study in healthy male volunteers (Gobburu et al. 1999) characterized GH release and PK, and ipamorelin reached Phase II trials for postoperative ileus. That program was discontinued because the trial showed no significant difference from placebo on the key efficacy endpoints. There are no large, long-term, peer-reviewed human trials demonstrating safety or benefit for body-composition, anti-aging, recovery, or "recomp" uses; claims in those areas are extrapolated from mechanism and animal data, not proven in controlled human studies. Caveats include very short follow-up in human data, small sample sizes, and a publication landscape skewed toward marketing-driven sources rather than independent clinical trials.

What is known about the safety of Ipamorelin?

In the short-term human and animal data available, ipamorelin was generally well tolerated; the Phase II ileus trial reported it was well tolerated over up to 7 days of dosing. Reported or plausible class effects of GH secretagogues include headache, flushing, injection-site reactions, transient increases in appetite (ghrelin-receptor effect), water retention, joint or muscle aches, and tingling/numbness. Stimulating the GH/IGF-1 axis carries theoretical risks of insulin resistance / impaired glucose tolerance and could be hazardous in people with active or prior malignancy because of GH/IGF-1 growth-promoting signaling. Long-term safety in humans is essentially unstudied. Because no approved standardized product exists, material sold outside licensed channels carries additional risks of impurity, mislabeling, incorrect potency, and contamination. Pregnancy, breastfeeding, and pediatric safety are not established.

What is the legal status of Ipamorelin?

Not approved by the FDA (or any major regulator) for any indication; it has no validated label, indication, or established benefit-risk profile. Clinical development for postoperative ileus was discontinued. In the United States it is not a controlled substance but is not a legally marketed drug; in September 2024 ipamorelin acetate was removed from Category 2 of the FDA interim 503A bulk drug substances list after the nomination was withdrawn, and the FDA's position is that it should not be used in compounding pending further review — meaning it lacks a clear legal compounding pathway. It is widely sold as a "research chemical / for research use only," which is not a lawful route for human administration. In sport, ipamorelin is prohibited at all times (in and out of competition) under WADA Prohibited List class S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) as a growth hormone secretagogue.

What is the half-life of Ipamorelin?

Approximately 2 hours terminal elimination half-life in healthy human volunteers after IV administration (Gobburu et al., 1999; dose-proportional PK, clearance ~0.078 L/h/kg, steady-state volume of distribution ~0.22 L/kg). GH release peaks early (~0.67 h) and declines exponentially.

Sources

1. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552-561.
2. Gobburu JV, Agersø H, Jusko WJ, Ynddal L. Pharmacokinetic-Pharmacodynamic Modeling of Ipamorelin, a Growth Hormone Releasing Peptide, in Human Volunteers. Pharm Res. 1999;16(9):1412-1416. PMID: 10496658.
3. Johansen PB, Hansen KT, Andersen JV, Johansen NL. Pharmacokinetic evaluation of ipamorelin and other peptidyl growth hormone secretagogues with emphasis on nasal absorption. Xenobiotica. 1998;28(11):1083-1092. PMID: 9879640.
4. Safety and Efficacy of Ipamorelin for Management of Post-Operative Ileus (Helsinn). ClinicalTrials.gov NCT00672074.
5. Ipamorelin — Wikipedia (overview with cited primary references: structure, developer Novo Nordisk/NNC 26-0161, discontinuation, doping status).
6. WADA Prohibited List — S2 Peptide Hormones, Growth Factors, Related Substances and Mimetics (GH secretagogues prohibited at all times).
7. FDA — Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act / PCAC briefing materials.