Overview
Ipamorelin is a synthetic pentapeptide that acts as a selective agonist at the growth hormone secretagogue receptor (GHSR) — the same receptor targeted by the endogenous hunger hormone ghrelin. Among the GHRPs (growth hormone-releasing peptides), ipamorelin is considered the most selective, stimulating GH release with minimal activation of the hypothalamic-pituitary-adrenal (HPA) axis — meaning significantly less cortisol and prolactin elevation compared to older GHRPs like GHRP-2 and GHRP-6.
This selectivity profile makes ipamorelin one of the most widely studied research peptides in the GH secretagogue class, and it is frequently paired with CJC-1295 to create a synergistic GH-releasing stack that addresses both the GHRH receptor and the ghrelin receptor simultaneously.
Mechanism of Action
GHSR (Ghrelin Receptor) Agonism: Ipamorelin binds to the growth hormone secretagogue receptor 1a (GHSR-1a), which is expressed on pituitary somatotrophs. Activation of this receptor triggers a calcium-mediated intracellular signaling cascade that stimulates GH secretion independently of the GHRH pathway.
Selectivity Advantage: Unlike GHRP-2 and GHRP-6, ipamorelin shows minimal cross-reactivity with receptors mediating cortisol and prolactin release. This translates to a cleaner pharmacological profile with fewer off-target effects.
Synergy with GHRH Analogs: When combined with a GHRH analog (CJC-1295 or Sermorelin), ipamorelin and the GHRH analog act on complementary pathways — GHRH-R and GHSR-1a — producing GH release greater than either peptide alone. This synergy is why the CJC-1295 + Ipamorelin combination is one of the most common research protocols.
Clinical Research & Evidence
Evidence Level: 🟠 EL3 — Animal and early human data; no Phase III trials
| Study | N | Key Finding |
|---|---|---|
| Raun et al. 1998 | Rat | Dose-dependent GH release; high specificity, no cortisol elevation |
| Aagaard et al. 1999 | Pig | Maintained GH secretion; bone mineral density preservation |
| Limited human data | N/A | Phase I tolerability data not published in major journals |
Mechanism validation: The key published data validates the mechanism and selectivity. Clinical trials have not been conducted to establish efficacy or safety for specific human health indications.
Research-Referenced Dosing Protocols
Animal-extrapolated. No validated human dosing protocol exists.
Standalone:
- 100–300 mcg subcutaneous injection, 1–3x daily
- Typically timed before sleep to amplify the physiological nocturnal GH pulse
With CJC-1295:
- Ipamorelin 100–200 mcg + CJC-1295 without DAC 100 mcg, once before bed
- Or Ipamorelin 100–200 mcg at time of weekly CJC-1295 with DAC injection
Side Effects & Contraindications
Reported:
- Water retention (less than with GHRP-2/6)
- Increased hunger (ghrelin receptor activity)
- Injection site reactions
- Tingling extremities (transient)
- Headache at higher doses
Compared to older GHRPs: Ipamorelin produces significantly less cortisol elevation, less prolactin stimulation, and less hunger than GHRP-2 or GHRP-6 — considered a safer selectivity profile.
Contraindications (theoretical):
- Active malignancy
- Insulin resistance / diabetes (GH elevation can worsen insulin sensitivity)
- Pregnancy
Legal & Regulatory Status
| Region | Status |
|---|---|
| United States | Not FDA approved; research chemical status |
| European Union | No EMA approval |
| WADA | Prohibited (GH secretagogues) |
Research Citations
- Raun K, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998.
- Aagaard NK, et al. Growth hormone secretagogues — mechanism and clinical use. Dan Med Bull. 1999.
- Bowers CY. GH-releasing peptide-2. Trends Endocrinol Metab. 1993 (background GHSR context).