Ipamorelin vs Hexarelin
Reviewed by the BestHealingPeptides Editorial Team ·
Ipamorelin and hexarelin are both growth-hormone-releasing peptides (GHRPs) acting as GHSR-1a agonists at the ghrelin receptor. They differ substantially in selectivity, potency, receptor kinetics, and off-target profile — hexarelin is more potent and engages the cardiac CD36 receptor; ipamorelin is more selective for GHSR-1a and has cleaner off-target pharmacology.
Ipamorelin
A pentapeptide GHRP (growth-hormone-releasing peptide) developed by Novo Nordisk in the 1990s, acting as a selective agonist of the GHSR (ghrelin receptor) on pituitary somatotrophs. Distinguished from other GHRP-class compounds by its high GH selectivity — minimal effects on cortisol, prolactin, ACTH, or aldosterone — making it the cleanest GHRP-class research tool when GH-pulse isolation is the experimental goal.
Hexarelin
A synthetic hexapeptide GHRP-class secretagogue developed by Mediolanum Farmaceutici (Italy) as an analogue of GHRP-6 with enhanced GH-releasing activity. Distinguished pharmacologically by producing the largest acute GH-releasing capacity of any GHRP at saturating doses and by direct binding to cardiac CD36 receptors — a unique cardiac-conditioning mechanism not shared by other GHRPs.
| Aspect | Ipamorelin | Hexarelin |
|---|---|---|
| Structure | Pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) | Hexapeptide (His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH2) |
| Primary receptor | GHSR-1a (selective) | GHSR-1a + CD36 |
| Relative potency at GHSR-1a | Standard reference | ~5-10x more potent |
| Off-target pharmacology | Minimal (clean profile) | Cardiac CD36 engagement |
| Desensitisation profile | Modest with chronic dosing | Rapid with chronic dosing |
| Typical research dose | 100-300 μg/dose | 25-100 μg/dose |
| Clinical-development history | Phase II (postoperative ileus, Helsinn) | Extensive Phase II GH-deficiency (1990s-2000s) |
| WADA status (2025) | Not listed | Not listed |
Mechanism
Both compounds are synthetic GHRPs that agonise GHSR-1a (the ghrelin receptor) on hypothalamic and pituitary somatotroph cells, producing pulsatile growth-hormone release with modest downstream IGF-1 elevation. Ipamorelin is a pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) with high selectivity for GHSR-1a and minimal off-target activity at prolactin, cortisol, or ACTH-releasing pathways. Hexarelin is a hexapeptide (His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH2) with substantially higher potency than ipamorelin at GHSR-1a but with additional agonism at CD36 — a scavenger receptor expressed on cardiomyocytes that mediates hexarelin's characteristic cardioprotective effects (and complicates its pharmacological profile relative to selective GHSR-1a agonists).
Potency and dosing implications
Hexarelin is approximately 5-10 times more potent than ipamorelin at GHSR-1a on a per-molar basis in in-vitro and in-vivo comparative work. Typical research doses reflect this potency difference: ipamorelin at 100-300 μg per dose vs hexarelin at 25-100 μg per dose in most published research protocols. The higher potency of hexarelin has translated less cleanly to clinical benefit than the raw receptor pharmacology suggests, because rapid desensitisation of GHSR-1a with repeated hexarelin dosing attenuates GH-releasing efficacy within days to weeks of sustained administration. Ipamorelin shows less pronounced desensitisation, supporting more prolonged research and clinical-development protocols.
Off-target pharmacology and safety differentiation
Ipamorelin's clean off-target profile is the compound's principal pharmacological differentiator — it does not appreciably elevate prolactin, cortisol, or ACTH at pharmacological doses, and it does not produce hexarelin's cardiac-CD36 engagement. This makes ipamorelin the preferred GHRP for research contexts where a defined-mechanism GHSR-1a interrogation is desired. Hexarelin's cardiac CD36 agonism has been characterised as cardioprotective in some contexts (post-ischaemic recovery models) but as complicating in others (chronic dosing produces morphological cardiac changes attributable to CD36-mediated fatty-acid uptake modulation). Neither compound is on WADA's Prohibited List as of 2025 iteration.
Clinical-development trajectory
Neither ipamorelin nor hexarelin has achieved marketing authorisation. Ipamorelin advanced through Phase II development for postoperative ileus (Helsinn Therapeutics) with encouraging efficacy but ultimately unsuccessful registration in the mid-2010s. Hexarelin was extensively evaluated in adult and paediatric GH-deficiency contexts across the 1990s and 2000s, with the desensitisation dynamics ultimately limiting clinical utility for chronic dosing. The broader GHRP class shifted focus to MK-677/ibutamoren (an orally-active non-peptide GHSR-1a agonist) for chronic-dosing applications; neither ipamorelin nor hexarelin has an active clinical-development programme at present.
Choosing between them (research context)
For research characterising the ghrelin/GHSR-1a axis, ipamorelin is the preferred selective tool given the clean off-target profile. For research specifically interrogating CD36-mediated cardiac pharmacology or acute high-magnitude GH-release characterisation, hexarelin's greater potency and CD36 engagement are pharmacologically informative. Combined use with a GHRH-analogue (CJC-1295) is the standard fleet approach — both GHRPs combine synergistically with GHRH agonists to produce larger physiological-pattern GH release than either monotherapy. Both compounds are research chemicals rather than clinical medicines.
Verdict
Ipamorelin is the selective, clean-profile GHRP preferred for research on the ghrelin/GHSR-1a axis without off-target confounds; hexarelin is the more potent, cardiac-CD36-engaging alternative preferred for high-magnitude GH-release studies or CD36-focused cardiac research. Ipamorelin is better suited to chronic-dosing protocols given attenuated desensitisation; hexarelin's rapid desensitisation limits sustained dosing utility.
Where to source research peptides for laboratory research
The following UK-based suppliers stock research-grade, lyophilised peptides for in-vitro and pre-clinical work. Purity and provenance vary; always request a Certificate of Analysis (CoA) and confirm cold-chain storage on arrival. None of the products linked below are approved for human use.
- PeptideAuthority.co.uk
UK-based research peptide supplier with batch certificates of analysis and >99% purity testing.
- PeptideBarn.co.uk
Wide catalogue of research-grade lyophilised peptides shipped from the UK, including bulk vials.