A 5-amino-acid synthetic peptide that selectively stimulates growth hormone release through the ghrelin/GHS receptor. Considered the 'cleanest' GH secretagogue because it does not significantly affect cortisol, prolactin, or aldosterone levels.
Ipamorelin is a synthetic pentapeptide growth hormone secretagogue (GHS) that acts on the ghrelin receptor (GHS-R1a) in the pituitary gland. It was developed by Novo Nordisk in the late 1990s and is notable for being the most selective GH secretagogue discovered — it stimulates GH release without significantly affecting cortisol, prolactin, ACTH, or aldosterone levels.
Ipamorelin is commonly combined with CJC-1295 in clinical peptide protocols. The rationale is complementary receptor targeting: CJC-1295 stimulates GH release through the GHRH receptor, while ipamorelin stimulates it through the ghrelin receptor. Together, they produce greater GH pulses than either peptide alone.
Ipamorelin is considered the most selective growth hormone secretagogue in its class. Unlike GHRP-6 and GHRP-2 (which also stimulate appetite, cortisol, and prolactin release), ipamorelin's selectivity for the GHS-R1a receptor means it produces a clean GH pulse without the unwanted hormonal side effects that limit other secretagogues. This selectivity is why it became the most widely prescribed GH peptide in functional medicine and why it is frequently paired with CJC-1295 (the "CJC/Ipa stack").
Originally developed by Novo Nordisk in the late 1990s, ipamorelin progressed through early clinical trials for post-operative ileus (paralysis of the bowel after surgery) but was not pursued to market approval. Despite this, its mechanism is well-characterized and its safety profile from clinical studies is favorable.
Ipamorelin was placed on the FDA's Category 2 list in late 2023. It is expected to return to Category 1 under the February 2026 HHS reclassification, though formal FDA guidance has not yet been published. See our March 2026 briefing for the latest status.
Ipamorelin binds to the GHS-R1a, a Gq-coupled GPCR primarily expressed on pituitary somatotrophs. Activation triggers PLC-mediated calcium release from intracellular stores, which promotes fusion of GH-containing secretory granules with the cell membrane. This pathway is independent of and synergistic with the GHRH-Gs-cAMP pathway (targeted by CJC-1295), which is why combining the two peptides produces amplified GH release.
| Pathway | Effect | Significance |
|---|---|---|
| Selective GH release | Activates GHS-R1a on somatotrophs without HPA axis activation | GH increase without cortisol, prolactin, or aldosterone changes |
| Preserved pulsatility | Amplifies natural GH pulses rather than creating flat elevation | More physiological GH profile than exogenous GH injection |
| Synergy with CJC-1295 | Ghrelin receptor + GHRH receptor dual stimulation | Greater GH amplitude than either peptide alone |
| Minimal hunger effect | Less ghrelin-like appetite stimulation than GHRP-6 | Better tolerated and fewer food cravings |
| IGF-1 increase | GH-mediated hepatic IGF-1 production | Downstream anabolic and repair effects |
| Study | Design | Findings | Level |
|---|---|---|---|
| GH release | Phase I/II, healthy volunteers | Dose-dependent GH increase; peak at 30-60 min post-injection; no significant cortisol or prolactin changes | Level II |
| Selectivity comparison | Preclinical + clinical | Ipamorelin is more selective than GHRP-6 (which increases cortisol and hunger) and GHRP-2 (which increases cortisol and prolactin) | Level II |
| Post-surgical recovery | Phase II, abdominal surgery | Improved GI recovery and reduced hospital stay in post-surgical patients | Level II |
| CJC-1295 combination | Clinical research | Synergistic GH release documented; commonly used protocol in anti-aging medicine | Level II-III |
Favorable selectivity: Ipamorelin's key safety advantage is its selectivity. At therapeutic doses, it does not significantly elevate cortisol, prolactin, or ACTH — side effects that limit the utility of older GH secretagogues like GHRP-6. This makes it suitable for longer-term protocols without the hormonal disruptions associated with less selective compounds.
GH-related side effects: Water retention, transient numbness or tingling, mild joint stiffness, and increased hunger have been reported, particularly at higher doses. These effects are GH-mediated and typically dose-dependent.
Head rush and flushing: Some users report a transient "head rush" or facial flushing immediately after injection, lasting 5-15 minutes. This is a known effect of ghrelin-receptor activation and is not considered clinically significant.
Clinical trial safety data: In Novo Nordisk's clinical studies for post-operative ileus, ipamorelin was well-tolerated with no serious adverse events attributed to the drug. The discontinuation rate due to adverse effects was comparable to placebo.
| Jurisdiction | Status |
|---|---|
| FDA | Not approved. Novo Nordisk discontinued clinical development. |
| WADA | Banned under S2 (Peptide hormones and growth factors) |
| Availability | Available as a research chemical |