Background
Before ipamorelin, all known GH secretagogues (GHRP-2, GHRP-6, hexarelin) produced significant cortisol and prolactin elevation alongside GH release — an undesirable effect profile for clinical use. The discovery of ipamorelin represented a major advance: GH selectivity without off-target axis activation.
This foundational paper by Raun et al. (Novo Nordisk) characterized ipamorelin’s pharmacological profile across multiple animal models and established the selectivity that made it attractive for clinical development and eventual peptide therapy use.
Methods
Series of rat and pig studies. GH, cortisol, prolactin, ACTH measured after single and repeated ipamorelin dosing vs. GHRP-6, hexarelin, and GHRP-2 (all at equimolar doses). Included dose-response curves, pulsatility assessment, and GH axis feedback evaluation.
Key Findings
| Hormone | Ipamorelin | GHRP-6 | Hexarelin | GHRP-2 |
|---|---|---|---|---|
| GH release | +++++ | +++++ | +++++ | +++++ |
| Cortisol elevation | None | ++ | +++ | +++ |
| Prolactin elevation | None | ++ | +++ | ++ |
| ACTH elevation | None | + | ++ | ++ |
Additional findings:
- Ipamorelin maintained pulsatile GH release (no blunting of natural pulses)
- Repeated administration: no tachyphylaxis (desensitization) at standard doses
- GH release was additive with GHRH — supporting combination CJC-1295/ipamorelin protocols
Clinical Significance
Ipamorelin’s cortisol and prolactin selectivity is its defining clinical advantage. Cortisol elevation with other GHRPs can counteract the anabolic and immune benefits of GH. Ipamorelin’s clean profile makes it the preferred GH secretagogue for anti-aging and recovery protocols where stress hormone avoidance is important.
This selectivity profile underpins the rationale for CJC-1295/ipamorelin combination therapy — combining GHRH-axis stimulation (CJC-1295) with selective GH pulse amplification (ipamorelin).
Limitations
- All data from animal models (rat and pig); no human pharmacokinetic or efficacy data in this paper
- Long-term effects in humans not characterized in controlled trials
- Human pituitary response may differ from animal models
- Dose translation to humans remains empirical