Both ipamorelin and GHRP-2 are GHSR-1a agonists (ghrelin mimetics), but ipamorelin is significantly more receptor-selective: it does not stimulate cortisol, ACTH, or prolactin at GH-releasing doses, while GHRP-2 produces modest elevations in all three.
Research reference only — all information on this page summarises peer-reviewed scientific literature and does not constitute medical advice. View full compound profiles: Ipamorelin · GHRP-2
Mechanism Comparison
Ipamorelin and GHRP-2 both activate the growth hormone secretagogue receptor 1a (GHSR-1a), triggering pituitary GH release via Gq/IP3 signalling. The key distinction is selectivity. GHRP-2 cross-activates ACTH and prolactin secretion — via hypothalamic-pituitary pathways separate from the direct GHSR-1a signal — resulting in measurable cortisol and prolactin elevations in research subjects. Ipamorelin, a pentapeptide GHS, shows markedly less off-target receptor activity, with published studies showing minimal cortisol or prolactin response at doses producing substantial GH release.
Side-by-Side Attributes
| Attribute | Ipamorelin | GHRP-2 |
|---|---|---|
| Receptor target | GHSR-1a (ghrelin receptor) | GHSR-1a (ghrelin receptor) |
| Peptide length | Pentapeptide (5 amino acids) | Hexapeptide (6 amino acids) |
| GH release potency | Moderate-high | High |
| Cortisol elevation in research | Minimal / not significant | Modest but significant |
| Prolactin elevation | Minimal | Modest |
| ACTH stimulation | Not significant | Present (secondary pathway) |
| Half-life | ~2 hours | ~1–2 hours |
| Appetite stimulation | Minimal (unlike ghrelin) | Present (ghrelin-like) |
| Selectivity designation in literature | Most selective GHS studied | Less selective; broader HPA-axis activity |
Key Research Points
- 1Ipamorelin is consistently described in the GHS literature as the most receptor-selective ghrelin mimetic studied — published dose-response research confirms minimal cortisol, ACTH, and prolactin stimulation at doses producing robust GH release.
- 2GHRP-2 produces greater peak GH release than ipamorelin at comparable molar doses in some published protocols, but this comes with measurable HPA-axis co-activation; researchers studying isolated GH axis effects must account for the cortisol confound.
- 3Appetite stimulation is a ghrelin receptor-downstream effect; GHRP-2 produces stronger appetite signalling (similar to ghrelin) while ipamorelin's appetite-stimulating effect is minimal, making it more suitable for protocols where food intake is a controlled variable.
- 4Both compounds are classified as GHSR-1a agonists ("ghrelin mimetics") and are 503A Category 2 compounds as of mid-2026, restricting their domestic compounding availability.
- 5Combination protocols frequently pair either compound with a GHRH analogue (CJC-1295 or sermorelin) to leverage synergistic GH release through co-activation of GHRH-R and GHSR-1a simultaneously.
Frequently Asked Questions
What is the main difference between ipamorelin and GHRP-2?
Both ipamorelin and GHRP-2 are GHSR-1a (ghrelin receptor) agonists that stimulate GH release from the pituitary. The primary difference is receptor selectivity: ipamorelin is the more selective compound, producing minimal elevations in cortisol, ACTH, and prolactin at GH-releasing doses. GHRP-2 stimulates GH comparably or slightly more potently but produces measurable cortisol and prolactin increases via secondary hypothalamic-pituitary pathways. For isolated GH axis research, ipamorelin's selectivity is its key advantage.
Does ipamorelin raise cortisol levels in research?
Published studies consistently show ipamorelin does not significantly elevate cortisol, ACTH, or prolactin at doses that produce robust GH release — unlike GHRP-2, GHRP-6, or hexarelin, which produce varying degrees of HPA-axis co-activation. This selectivity profile was established in early characterisation studies (Raun et al., European Journal of Endocrinology, 1998) and has been reproduced in subsequent research. It makes ipamorelin the preferred GHSR-1a tool when researchers need to isolate GH effects from glucocorticoid confounding.
Which is more potent for GH release — ipamorelin or GHRP-2?
GHRP-2 typically produces slightly greater peak GH elevation than ipamorelin at comparable doses in published protocols. However, "potency" in this context must be weighed against selectivity: GHRP-2's greater GH release comes with cortisol, prolactin, and ACTH co-stimulation that can confound experimental results in protocols studying GH-mediated tissue effects. For research requiring clean GH axis activation without HPA co-activation, ipamorelin's moderate potency with high selectivity is preferable.
Deep Dive
For extended mechanism analysis, trial data, and regulatory context, see the full research article:
Ipamorelin vs GHRP-2 vs GHRP-6: GH Secretagogue Comparison →Full compound profile
Ipamorelin
Full compound profile
GHRP-2