Mechanism of Action
Ipamorelin acts as a selective agonist at the growth hormone secretagogue receptor (GHSR-1a), the ghrelin/" class="wiki-internal-link">ghrelin receptor expressed on pituitary somatotrophs.
Selective Ghrelin Receptor Agonism
Ipamorelin binds GHSR-1a with high affinity, stimulating pulsatile GH release. Unlike the endogenous ligand ghrelin, Ipamorelin does not activate hypothalamic circuits that drive appetite or cortisol/acth/" class="wiki-internal-link">ACTH release. This selectivity is its primary clinical advantage over first-generation GHRPs.[1]GHRH Synergy
Ipamorelin works synergistically with growth hormone releasing hormone (GHRH) and its analogs (CJC-1295, Mod GRF 1-29). GHRH amplifies the GH pulse amplitude while Ipamorelin provides the receptor stimulus, together producing a GH pulse 2-10x larger than either alone.[2]Pulsatile vs. Continuous GH Elevation
Ipamorelin produces discrete GH pulses (peaks at ~60 min, returns to baseline by ~3 hours) rather than sustained elevation. This pulsatile pattern more closely resembles physiological GH secretion than continuous GH agonists, which is associated with a more favorable side effect profile and maintained GH receptor sensitivity.[1]Research Overview
GH Secretion and IGF-1 Elevation
Most StudiedIpamorelin produces dose-dependent GH release with minimal off-target effects. At 100-300 mcg subcutaneous doses, GH peaks at 60-90 minutes. Chronic use elevates baseline IGF-1 levels, with studies showing 25-50% increases in IGF-1 over 4-8 week protocols.[1]
Postoperative Recovery
Phase II ClinicalIpamorelin (INN: ulimorelin) has been evaluated in Phase II/III trials for postoperative ileus. Results show accelerated GI motility recovery and reduced hospital stay. This GI effect is mediated through peripheral GHSR-1a activation in enteric neurons independent of GH release.[3]
Body Composition
Moderate EvidenceGH elevation from Ipamorelin protocols increases lipolysis and may support lean mass preservation. Studies in aging rodents show reduction in fat mass and maintenance of muscle mass with chronic administration. Human body composition data is limited to observational reports.[2]
Bone Density
Moderate EvidenceGHRP stimulation of the GH/IGF-1 axis increases bone mineral density in animal models of growth hormone deficiency. Ipamorelin shows bone density improvements in rats given 4-week protocols at relevant doses.[4]
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Clinical Trial Data
| Phase | Trial | N | Duration | Key Outcome |
|---|---|---|---|---|
| Phase 2 | Raun et al. GH selectivity (NNC 26-0161) PMID:12814945 | 9 | Acute crossover | Selective pulsatile GH elevation without cortisol, ACTH, or prolactin changes; dose-dependent GH secretion confirmed |
| Phase 2 | Postoperative ileus (ulimorelin) PMID:21228936 | 460 | 5 days | Accelerated GI motility recovery post-colorectal surgery; reduced time to first bowel movement |
| Phase 1 | Porcine GH axis characterization PMID:15741266 | Preclinical | Acute | Dose-dependent GH secretion; receptor specificity for GHSR-1a confirmed; selectivity profile superior to GHRP-2, GHRP-6 |
Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| GH pulse / recovery | 200–300 µg | 1× daily (before bed) | Subcutaneous |
| Stacked with CJC-1295 | 100–200 µg Ipamorelin | 2–3× daily | Subcutaneous |
| Conservative start | 100 µg | 1× daily | Subcutaneous |
| Body composition | 200 µg | 2× daily (AM / before bed) | Subcutaneous |
Bedtime dosing capitalizes on natural GH secretion during deep sleep. Fasted administration (2-3 hours post-meal) maximizes GH pulse amplitude, food intake (especially carbohydrates) blunts GH response via somatostatin. When stacking with CJC-1295, administer simultaneously for maximum synergy.
Research protocols only. Not medical advice.
Peptide Interactions
Safety Profile
Ipamorelin has a favorable safety profile compared to other GHRPs, primarily due to its selectivity. Phase II clinical trials confirm safety at doses up to 1600 mcg/day.
WADA Status: Prohibited by WADA as a peptide hormone and growth factor. Athletes subject to testing must not use this compound.
Water retention: Mild fluid retention is common with GH-axis peptides. This typically resolves within days of discontinuation.
IGF-1 monitoring: Prolonged GH/IGF-1 elevation raises theoretical concerns about insulin resistance and cell proliferation. Periodic IGF-1 monitoring is recommended for long-duration protocols.
Selectively advantaged: Unlike GHRP-2 and Hexarelin, Ipamorelin does not meaningfully raise cortisol, prolactin, or appetite hormones at research doses.
Allergic reactions: Rare but documented in anecdotal reports — hot skin, itching, flushing, or heart palpitations after injection. The suspected culprit in some cases may be the GHRH component (Mod-GRF/CJC-1295) rather than Ipamorelin itself. If symptoms occur, stop immediately. Always begin with a very low test dose (50 µg) when first using any GH secretagogue.
No FDA approval: Not approved for human therapeutic use outside of Phase II research.
References
- [1]Raun K, et al. "Ipamorelin, the first selective growth hormone secretagogue." Eur J Endocrinol. 1998;139(5):552-561. PMID:9803244
- [2]Johansen PB, et al. "Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats." Growth Horm IGF Res. 1999;9(2):106-113. PMID:10372582
- [3]Sanger GJ, et al. "Motilin and Erythromycin, and Ghrelin and Its Receptor Agonists." Curr Opin Pharmacol. 2013;13(6):870-876. PMID:24060217
- [4]Hansen TK, et al. "Serum IGF-I and growth hormone secretagogue receptor expression in bone marrow." Horm Res. 2003;60(6):261-270. PMID:14651263