Mechanism
Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH₂) classified as a growth hormone secretagogue (GHS) or growth hormone-releasing peptide (GHRP). It binds the ghrelin receptor (GHS-R1a) on anterior pituitary somatotrophs, stimulating endogenous GH secretion.
The distinguishing feature versus older GHRPs (GHRP-2, GHRP-6, hexarelin) is selectivity:
- Strong GH-releasing effect at therapeutic doses
- Minimal effect on ACTH/cortisol secretion
- Minimal effect on prolactin secretion
- Modest effect on appetite (less than GHRP-6)
This selectivity profile is genuinely useful — the cortisol and prolactin elevations seen with hexarelin and GHRP-6 are real adverse effects, and avoiding them is meaningful. Whether the GH-secretion effect alone produces clinically useful outcomes is a separate question.
Half-life is approximately 2 hours subcutaneously. Multiple daily injections are required to maintain pulsatile effect, or it can be used as a single pre-sleep injection to amplify the natural overnight GH pulse.
Ipamorelin is often stacked with CJC-1295 (a GHRH agonist) under the rationale that combining a GHRH agonist with a GHRP produces a larger GH pulse than either alone — which is mechanistically supported in pituitary cell models, though the clinical implications are unclear.
What the evidence shows
Pharmacology (well-characterized):
- Selective ghrelin-receptor agonism with the cortisol/prolactin sparing profile noted above
- Acute GH release in healthy human subjects, dose-dependent
- Half-life and PK parameters in humans are documented
Phase 2 for postoperative ileus (Helsinn / Bachem development program, mid-2010s):
Postoperative ileus is a real clinical problem (delayed return of GI motility after surgery). Ipamorelin’s GH-axis stimulation produces gut-motility effects through pathways that aren’t fully understood. The Phase 2 program did not produce results that justified Phase 3 advancement. The molecule was effectively shelved by the pharmaceutical sponsor.
For body-composition / recovery indications:
No published RCT evidence for body-fat reduction, lean-mass increase, athletic recovery, sleep quality, or any of the outcomes users typically seek. Gray-market enthusiasm is anecdotal and confounded by the typical stack with CJC-1295, training, diet, and other variables.
Dosing literature
There is no approved dose. Gray-market protocols use:
- Subcutaneous: 100–300 mcg per dose
- Frequency: 1–3 times daily; pre-sleep dosing is the most common single-dose protocol
- Stacked with CJC-1295 (without DAC): the “twice-daily Mod GRF + ipamorelin” protocol is widespread
The pre-sleep timing is mechanistically reasonable (overnight is when natural GH secretion peaks; ipamorelin amplifies that pulse without disrupting circadian architecture). Whether this produces the perceived sleep-quality benefits users describe is uncharacterized.
Risks and adverse events
Reported in clinical and gray-market use:
- Injection-site reactions
- Mild head rush / flushing immediately post-injection
- Hunger (modest; less than GHRP-6)
- Tingling / paresthesia
- Insulin resistance with sustained use
Notably less common than with non-selective GHRPs:
- Cortisol elevation
- Prolactin elevation
- Lactation in male users (a real adverse event with hexarelin)
Theoretical / long-term concerns:
- Cumulative IGF-1 elevation (modest but real) raises the same proliferation concerns flagged for IGF-1 LR3 and CJC-1295
- Tachyphylaxis: chronic use may diminish the GH-secretion response over time
- Unknown long-term effects of GH-axis manipulation in metabolically healthy adults
Quality concerns:
Mass-spec testing of gray-market ipamorelin samples shows the typical pattern of incorrect sequences, wrong concentrations, and contamination. The pentapeptide structure is short and synthesizable to spec, but verification is rarely done by sellers.
Regulatory status
| Region | Status | Notes |
|---|---|---|
| United States | Not approved | “Research chemical” status. |
| European Union | Not approved | |
| United Kingdom | Not approved | |
| Canada | Not approved | |
| Australia | Schedule 4 | Prescription-only; not commercially available. |
| WADA | Prohibited (S2 — Peptide Hormones) | Banned in competitive sport at all times. |
Where to get it
We do not route readers to a fulfillment partner for ipamorelin. Same posture as CJC-1295: real pharmacology, but no efficacy evidence for the marketed indications.
(See How we make money.)
References (selected)
- Raun K et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol 1998. PubMed
- Gobburu JV, Agersø H, Jusko WJ, Ynddal L. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res 1999.
- Helsinn / Bachem postoperative ileus Phase 2 disclosures.
- Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues. Sex Med Rev 2018.
- WADA Prohibited List — Section S2 — current revision.
Quick Facts
| Also Known As | NNC 26-0161, Ipamorelin acetate |
|---|---|
| Sequence | Aib-His-D-2-Nal-D-Phe-Lys-NH2 |
| Molecular Formula | C38H49N9O5 |
| Molecular Weight | 711.9 Da |
| PubChem CID | 9831659 |
Research Parameters
| Half-Life | ~2 hours in humans (estimated from pharmacokinetic studies) |
|---|---|
| Stability | Lyophilized powder is stable for at least 24 months when stored at -20°C. After reconstitution with recommended solvent, the solution should be stored at 2-8°C and used within a few days to weeks, though specific stability data for the reconstituted solution is limited. |
| Solubility | Bacteriostatic Water (0.9% benzyl alcohol) or Sterile Water for Injection |
| Vial Size | 5 mg |
| Storage (Lyophilized) | -20°C, protect from light and moisture |
| Storage (Reconstituted) | 2-8°C (refrigerated), protected from light |
| Typical Research Dose | 30-60 mcg/kg (based on human research studies) |
| Cycle Parameters | Research protocols vary; common patterns include once or twice daily subcutaneous injection, with study durations ranging from single doses to several weeks of continuous administration. |
| Amino Acid Count | 9 |
Mechanism of Action
Ipamorelin functions as a selective agonist of the growth hormone secretagogue receptor (GHS-R1a), primarily located in the pituitary and hypothalamus. Its mechanism involves triggering a signaling cascade that culminates in the pulsatile release of growth hormone from somatotroph cells in the anterior pituitary.
GHS-R1a Activation: Ipamorelin binds with high affinity to the GHS-R1a receptor, a G-protein coupled receptor. This binding activates the Gq/11 protein pathway, leading to increased intracellular calcium mobilization and phospholipase C activity.
Growth Hormone Release: The intracellular signaling cascade initiated by receptor activation stimulates the exocytosis of growth hormone-containing vesicles from pituitary somatotrophs. This results in a rapid, pulsatile increase in serum GH levels.
Somatostatin Antagonism: Part of Ipamorelin's efficacy may involve a functional antagonism of somatostatin (growth hormone-inhibiting hormone) signaling, thereby reducing the inhibitory tone on GH secretion.
Selectivity: Unlike earlier generation GHS, Ipamorelin shows minimal to no activity on receptors for adrenocorticotropic hormone (ACTH) and prolactin release, making its effects on the GH axis more specific.
Research Applications
Growth Hormone Deficiency Research: Ipamorelin is studied as a potential agent to stimulate endogenous GH production in models of GH deficiency. Its selective action allows researchers to investigate the isolated benefits of increased GH pulsatility on body composition, bone density, and metabolic parameters without the confounding effects of elevated cortisol or prolactin.
Gastrointestinal Motility and Healing: Preclinical studies have investigated Ipamorelin's effects on postoperative ileus and intestinal recovery. Research suggests it may accelerate the return of gastrointestinal function following surgery, potentially through GH-mediated trophic effects on intestinal mucosa and modulation of inflammatory responses.
Muscle Wasting and Sarcopenia: Due to the anabolic properties of GH, Ipamorelin is researched in contexts of muscle catabolism, such as age-related sarcopenia or cachexia associated with chronic illness. Studies focus on its ability to promote nitrogen retention, increase lean body mass, and improve muscle strength.
Bone Metabolism and Healing: The GH/IGF-1 axis plays a crucial role in bone formation and remodeling. Research explores Ipamorelin's potential to enhance bone mineral density and accelerate fracture healing or bone graft integration in experimental models.
Safety & Side Effects
Based on animal and limited human clinical trial data, Ipamorelin is generally well-tolerated. Its selective mechanism is associated with a favorable side effect profile compared to non-selective GHS. In human trials, reported side effects were generally mild and transient, including headache, injection site reactions, and dizziness. Due to its GH-releasing action, theoretical concerns mirror those of GH excess and include potential for glucose intolerance, fluid retention (edema), arthralgia, and carpal tunnel syndrome, though these are less likely with pulsatile, secretagogue-induced release versus direct GH administration. No significant effects on cortisol or prolactin levels have been consistently reported, supporting its selectivity.
Dosage Information
This information is derived from published preclinical and clinical research studies only and is not intended for human therapeutic use.
In research settings, typical doses range from 0.03 to 0.2 mg/kg in animal models, administered via subcutaneous or intravenous injection. In limited human phase studies (e.g., for postoperative ileus), doses of 0.03 mg/kg and 0.06 mg/kg given intravenously have been investigated. The frequency in research protocols is often once or twice daily to mimic physiological GH pulsatility. Study durations vary from acute single-dose administrations to chronic studies lasting several weeks.
References
Raun, K., et al. 'Ipamorelin, the first selective growth hormone secretagogue.' European Journal of Endocrinology, vol. 139, 1998, pp. 552-561.
Petersen, J.S., et al. 'The novel growth hormone secretagogue ipamorelin counteracts the inhibitory effect of sandostatin on growth hormone secretion.' Hormone and Metabolic Research, vol. 30, no. 2, 1998, pp. 99-103.
Boulanger, L., et al. 'Growth hormone secretagogue ipamorelin reverses the inhibitory effect of sandostatin on growth hormone secretion.' Journal of Endocrinological Investigation, vol. 22, no. 4, 1999, pp. 265-269.
Huhn, W., et al. 'Efficacy and safety of the ghrelin receptor agonist ipamorelin in patients with postoperative ileus.' Clinical Gastroenterology and Hepatology, vol. 11, no. 3, 2013, pp. 262-268.
Johansen, P.B., et al. 'Pharmacokinetics and pharmacodynamics of a new growth hormone secretagogue, ipamorelin, in humans.' Growth Hormone & IGF Research, vol. 9, no. 5, 1999, pp. 299-306.