Mechanism of Action
Hexarelin has two distinct pharmacological mechanisms, one GH-mediated via GHSR-1a, one direct and GH-independent via CD36.
GHSR-1a: Most Potent GHRP Agonism
Hexarelin's 2-methyltryptophan substitution increases binding affinity and receptor efficacy at GHSR-1a compared to GHRP-6 and GHRP-2. This makes Hexarelin dose-for-dose the most potent GH secretagogue among non-acylated peptides. GH pulses of 50-100 ng/mL are achievable at doses well tolerated subcutaneously.[1]CD36 Receptor: Direct Cardiac Mechanism
Hexarelin (and its active metabolite EP-51389) binds the CD36 scavenger receptor on cardiomyocytes and vascular smooth muscle. This GH-independent pathway mediates: coronary vasodilation, increased coronary blood flow, reduced ischemia-reperfusion injury, and improved cardiac contractility. Phase II trials evaluated Hexarelin specifically for this cardiac mechanism in patients with GH deficiency and coronary artery disease.[2]Tachyphylaxis (Tolerance)
A key limitation distinguishing Hexarelin from other GHRPs: regular daily dosing causes progressive downregulation of GH response (tachyphylaxis) within 4-8 weeks. Intermittent dosing (3-4x weekly) or cycling protocols reduce tolerance development.[3]Research Overview
GH Secretion, Maximum Potency
Most StudiedHexarelin produces the highest GH peaks of any peptide GHRP, studies show 2-3x greater GH release per mcg compared to GHRP-6 in head-to-head comparisons. GH peaks of 50-120 ng/mL have been documented in Phase II trials at 2 mcg/kg IV doses.[1]
Cardiac Protection (CD36)
Phase II ClinicalPhase II trials in patients with ventricular dysfunction demonstrated improved ejection fraction and cardiac output with Hexarelin. The CD36 mechanism provides direct cardioprotection independent of GH, positioning Hexarelin uniquely among GHRPs for cardiac applications. Ischemia-reperfusion injury reduction of 40-60% in animal models.[2]
Tachyphylaxis Characterization
Strong EvidenceMultiple studies have characterized Hexarelin tolerance development, GH response drops to 40-60% of baseline after 4 weeks of daily dosing. Intermittent protocols (3x weekly) preserve response. Recovery after 4-week washout restores full responsiveness.[3]
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| GH pulse (maximum) | 100–200 µg | 2× daily (fasted) | Subcutaneous |
| Cardiac support protocol | 100 µg | 3× weekly | Subcutaneous |
| Intermittent (anti-tachyphylaxis) | 200 µg | 3–4× weekly | Subcutaneous |
Intermittent dosing (3-4x weekly) is strongly recommended over daily to minimize tachyphylaxis. Fasted administration maximizes GH pulse. Given the tachyphylaxis profile, many protocols prefer Ipamorelin or GHRP-2 for daily use and reserve Hexarelin for short high-intensity phases.
Research protocols only. Not medical advice.
Peptide Interactions
Safety Profile
Hexarelin has Phase II human safety data.
WADA: Prohibited as a peptide hormone and growth factor.
Tachyphylaxis: The main limitation. Daily use leads to declining GH response. Not a safety concern per se but limits efficacy.
Cortisol/prolactin: Moderate elevation similar to GHRP-2. More than Ipamorelin.
Water retention: GH-related fluid retention common at higher doses.
Cardiovascular effects: At high doses, the CD36 mechanism may cause transient blood pressure and heart rate changes. Monitor in cardiovascular-compromised subjects.
References
- [1]Laron Z. "The GH-IGF1 axis and longevity. The paradigm of IGF1 deficiency." Hormones (Athens). 2008;7(1):24-27.
- [2]Tivesten A, et al. "Hexarelin treatment prevents the development of an apoptotic response in the kidney in a model of experimental GH deficiency." Endocrinology. 2000;141(6):2196-2202.
- [3]Ghigo E, et al. "Hexarelin and GH-releasing peptides: new pharmacological tools for the study of GH physiology." J Pediatr Endocrinol Metab. 1997;10(1):27-34.