Educational reference only. Informational material drawn from peer-reviewed literature. Not medical advice and not a recommendation to use, dose, or modify any therapy. Decisions about hormone therapy should be made with a qualified healthcare provider.
Overview
Overview
Ipamorelin is a synthetic pentapeptide (5 amino acids) that functions as a selective growth hormone secretagogue receptor (GHS-R1a) agonist, meaning it activates the receptor for ghrelin, the endogenous "hunger hormone." It belongs to the class of growth hormone releasing peptides (GHRPs) alongside GHRP-2, GHRP-6, and hexarelin, but is distinguished by its uniquely clean selectivity profile: ipamorelin stimulates GH release through ghrelin receptor activation without meaningfully elevating cortisol, prolactin, or ACTH at physiological doses. This is the defining characteristic that has made ipamorelin the most popular GHRP in clinical and non-medical use.
Ipamorelin has a substantial pharmaceutical history. It was developed by Novo Nordisk in the late 1990s (under the code name NNC 26-0161) and was the first synthetic growth hormone secretagogue to selectively release GH without significant ACTH, cortisol, or prolactin elevation. The compound progressed through Phase 2 clinical trials for postoperative ileus (gut motility after surgery) before development was discontinued, primarily due to lack of efficacy in that specific indication, rather than safety concerns (an important distinction from CJC-1295).
Different receptor class from sermorelin/CJC-1295: ipamorelin acts on the GHS-R1a (ghrelin receptor), while sermorelin and CJC-1295 act on the GHRH receptor. The two receptors sit on the same pituitary somatotrophs and stimulating both together has been studied.
Forms
Available forms & half-lives
| Form | Approximate half-life |
|---|---|
| Subcutaneous ipamorelin | ~2 hours |
What it does
Main effects
- Selective GH release via GHS-R1a (ghrelin receptor) activation: pulsatile GH release; peak at 30–40 minutes post-injection; 2–5× elevation in serum GH at peak PMID: 9849822
- "The first selective growth hormone secretagogue": unique selectivity profile is the defining feature; minimal effects on cortisol, prolactin, ACTH, and appetite at physiological doses
- Acts at a different receptor from the GHRH analogs (sermorelin, Mod GRF 1-29, CJC-1295): GHS-R1a rather than the GHRH receptor, on the same pituitary somatotrophs; stimulating both receptors together has been studied
- Preserved pulsatile GH release pattern: maintains physiological feedback regulation; unlike CJC-1295 with DAC which produces sustained elevation
- Counteracts glucocorticoid-induced bone loss in animal models: theoretical significance for patients on chronic corticosteroid therapy
- Dose-dependent longitudinal bone growth in animal models
- IGF-1 elevation with chronic use: less dramatic than with continuous GHRH stimulation
- Anti-aging / body composition (non-medical use): widely used; no controlled trial evidence for these indications
- Most rigorous published human evidence is the Phase 2 postoperative ileus trial PMID: 25331030: primary efficacy endpoint NOT met but ipamorelin was well tolerated
What to watch for
Common side effects
- Injection site reactions (pain, redness, swelling): most common adverse effect; mild and self-limited
- Mild constitutional symptoms (flushing common with initial doses, occasional headache, drowsiness with bedtime dosing, occasional dizziness)
- Selectivity advantages (what doesn't happen): no significant cortisol elevation (avoids weight gain, mood effects, immunosuppression), no significant prolactin elevation (avoids galactorrhea, gynecomastia, sexual dysfunction), minimal appetite stimulation (unlike GHRP-6), no significant ACTH elevation
- Mild insulin resistance: possible with sustained use; generally less significant than direct GH or sustained-elevation compounds (CJC-1295 with DAC)
- IGF-1 elevation: monitoring recommended to avoid excessive elevation
- Sleep effects: variable; some users report improved sleep quality with bedtime dosing; vivid dreams reported
- No significant cardiovascular adverse effects documented in clinical trials: less concerning than CJC-1295 (which has the halted Phase 2 trial history)
- Limited long-term safety data: Phase 2 trial provided short-term safety data (up to 7 days); substantial non-medical use experience suggests generally good tolerability but not systematically tracked
- Combined use with a GHRH analog (CJC-1295, sermorelin) has never been studied in a controlled clinical trial despite widespread non-medical use
- No published human efficacy trials for anti-aging, body composition, or GH deficiency: the pharmaceutical evidence base is for postoperative ileus (failed) and PK/PD characterization, not for the indications driving non-medical use
- WADA-prohibited under category S2; US Anti-Doping Agency, NFL, NBA, MLB, NHL, and NCAA all prohibit GHS-R1a agonists
- Product identity and purity are not guaranteed: with no approved product, what is supplied can vary in identity, purity, concentration and sterility for injectable use
Key facts
Key facts worth knowing
- Ipamorelin is a pentapeptide with sequence Aib-His-D-2-Nal-D-Phe-Lys-NH₂ (5 amino acids, MW 711.85 Da). It was first described by Raun et al. 1998 in European Journal of Endocrinology as "the first selective growth hormone secretagogue." PMID: 9849822
- Selectivity profile is the defining feature. Unlike GHRP-6 (significant appetite stimulation, cortisol/prolactin elevation), GHRP-2 (moderate cortisol/prolactin elevation), and hexarelin (significant cortisol/prolactin elevation, possible tachyphylaxis), ipamorelin produces GH release with minimal effects on other pituitary hormones. This makes it pharmacologically the "cleanest" GHRP.
- Mechanism is GHS-R1a (ghrelin receptor) agonism on pituitary somatotrophs. This is a different receptor than GHRH receptor (target of sermorelin and CJC-1295). Both receptors sit on the same somatotrophs, and stimulating them together has been studied.
- No ACTH/cortisol elevation at physiological doses: Unlike older GHRPs, ipamorelin does not activate the adrenocortical axis at typical doses. This avoids the cortisol-related side effects (weight gain, mood effects, immunosuppression) of other GHRPs. No prolactin elevation: Avoids galactorrhea, gynecomastia, sexual dysfunction. Minimal appetite stimulation: Unlike GHRP-6.
- Phase 2 trial (Beck et al. 2014) evaluated ipamorelin in 87 bowel resection patients for postoperative ileus. Primary efficacy endpoint not met: ipamorelin did not significantly reduce time to bowel function recovery vs placebo. Was well tolerated. This is the most rigorous published human ipamorelin study. PMID: 25331030
- Novo Nordisk discontinued development after the failed postoperative ileus indication. The compound was not pursued for other indications, likely because of commercial development decisions rather than safety concerns, a meaningful distinction from CJC-1295's halted development.
- No controlled trial has evaluated ipamorelin together with a GHRH analog. The two act at different receptors on the same somatotrophs, and the combination is used in non-medical contexts, but the combination itself has never been tested in a controlled trial.
- WADA Prohibited under category S2. Both ipamorelin and other GHRPs banned in and out of competition. US Anti-Doping Agency follows WADA. Major US professional leagues (NFL, NBA, MLB, NHL) and the NCAA prohibit GHS-R1a agonists.
Legal status
Legal status
No FDA approval. Phase 2 development discontinued by Novo Nordisk after primary efficacy endpoint not met in postoperative ileus trial (safety was acceptable). Available through 503A/503B compounding pharmacies (status evolving) and unregulated sources. Not a controlled substance. WADA-prohibited under category S2.