Hexarelin and the GHRP Family: A Comparison
The growth-hormone-releasing peptide family is a small set of ghrelin-mimetic peptides with different selectivity profiles. Hexarelin is the workhorse of the cardiovascular research subplot; ipamorelin is the cleanest profile; GHRP-2 and GHRP-6 sit between.
all GHRPs act on the ghrelin receptor (GHSR-1a) on pituitary somatotropes.
hexarelin is the GHRP most studied for cardiovascular effects via non-GH-related receptor binding (CD36).
ipamorelin selected for minimal prolactin and cortisol stimulation vs older GHRPs.
GHRP-6 is notable for inducing notable appetite increase (ghrelin-like effect).
The GHRP family — hexarelin, GHRP-2, GHRP-6 and ipamorelin — are synthetic ghrelin-receptor agonists that elicit pituitary GH release. The molecules differ in selectivity for downstream effects: GHRP-6 has the most ghrelin-like appetite effect, GHRP-2 less so, ipamorelin minimal prolactin/cortisol effect, and hexarelin has the most extensive cardiovascular research literature via non-pituitary receptor interactions (notably CD36). None are approved medicines; all are WADA-prohibited.
Same receptor family, different selectivity profiles, different research subplots. Treating them as interchangeable misses what's interesting about each.
The family overview
All GHRPs are synthetic peptide agonists at the ghrelin receptor (GHSR-1a) on pituitary somatotropes. Binding produces GH release via a mechanism distinct from but synergistic with GHRH.
The four most-studied family members are hexarelin (the most pharmacologically explored), GHRP-2 (commercial development for short stature historically), GHRP-6 (notable for ghrelin-like appetite effect), and ipamorelin (designed for selectivity, minimal prolactin/cortisol).
Hexarelin has the additional research interest of binding CD36 — a non-pituitary receptor expressed in cardiovascular tissue — which underlies a substantial cardiovascular research literature distinct from GH release.
Selectivity differences
| Layer | What the research describes |
|---|---|
| Hexarelin | Potent GHSR-1a agonist; additional CD36 binding underlies cardiovascular research interest. |
| GHRP-2 | Potent GHSR-1a agonist; some prolactin and cortisol stimulation. |
| GHRP-6 | GHSR-1a agonist with the most ghrelin-like appetite-increase effect. |
| Ipamorelin | GHSR-1a agonist selected for minimal prolactin and cortisol stimulation. |
| Pulse profile | All produce GH pulses; magnitude and frequency-of-administration profile differ. |
Subtle selectivity differences matter more than they appear. The 'cleanest' profile (ipamorelin) is not always the most pharmacologically interesting; the 'dirtiest' (hexarelin via CD36) carries a distinct cardiovascular subplot.
What the research literature contains
Pituitary GH release
Documented across all four molecules in pharmacological studies; magnitude and dose-response curves differ.
Hexarelin / CD36 / cardiovascular
Hexarelin has a substantial cardiovascular research literature — protective effects in ischaemia-reperfusion models — attributed to CD36 binding rather than GH release.
Clinical development
GHRP-2 reached clinical development for short stature; none of the family has achieved major regulatory approval for general indications.
Hexarelin's CD36-mediated cardiovascular subplot is genuinely interesting and structurally distinct from the rest of the family. It is also less well-translated to human clinical outcomes than the mechanism alone would suggest.
Across the family, the gap between pharmacological GH-release evidence and clinical-outcome evidence is similar — and similar to the CJC-1295/ipamorelin story discussed elsewhere on this blog.
What we know, what's still open
- GH release: Well-documented across all four molecules.
- Cardiovascular (hexarelin): Animal evidence interesting; human clinical translation thinner.
- Body composition outcomes: Limited published human evidence specific to GHRPs alone.
- Long-term safety: Not established at trial scale.
- Regulatory status: None approved; all WADA-prohibited under S2.
Frequently asked
Which is the 'best' GHRP?
Depends what you're asking. Selectivity (ipamorelin), GH pulse magnitude (GHRP-2 or hexarelin), cardiovascular research interest (hexarelin), appetite effect (GHRP-6) all differ. There is no single best.
Are they interchangeable?
No — the selectivity differences matter, and the research literatures differ enough that picking one based on another's evidence would be a mistake.
Why isn't hexarelin in cardiovascular medicine?
Animal data are interesting but the human cardiovascular outcomes evidence base is much smaller than for established cardioprotective drug classes.
Are they legal?
Research-compound grey zone in most jurisdictions; prohibited in tested sport under WADA S2. See our EU peptide legality reference.
Where to read further
- • Sigalos JT, Pastuszak AW. Safety and efficacy of GH secretagogues. Sex Med Rev 2018.
- • Bodart V et al. Hexarelin and CD36 cardiovascular research.
- • Raun K et al. Ipamorelin design rationale. Eur J Endocrinol 1998.