PwPepwise

Hexarelin

Growth Hormone

Potent GHRP

Hexarelin is a synthetic six-amino-acid peptide developed as a growth hormone secretagogue — a compound.

§Dosing at a glance

5 protocols · from the research
What it's forDoseHow oftenHowFor how long
into a vein (IV) administration0.50–0.64 mcg/kg———
under the skin (SC) administration1.5–3.0 mcg/kg———
into the nose administration20 mcg/kg—IntranasalSprayed into the nose.—
Oral administration10–40 mg—OralTaken by mouth.—
Age-related dosing considerations2 mcg/kg———

Approximate values pulled from the research — double-check before dosing.

§01Summary

Hexarelin is a synthetic six-amino-acid peptide developed as a growth hormone secretagogue — a compound that stimulates the body to release growth hormone (GH). It works primarily by activating a receptor in the brain and pituitary gland that responds to ghrelin, the body's natural hunger and GH-release signal. In clinical studies, hexarelin has consistently stimulated robust GH release across a wide range of doses and administration routes, including intravenous, subcutaneous, and even oral delivery10. Beyond GH release, hexarelin appears to have direct effects on the heart that are independent of GH, with early human studies reporting improved cardiac pumping function7. It may also stimulate the release of other hormones including cortisol and prolactin6, and has been reported to activate bone-forming cells17 and inhibit fat breakdown in preclinical models16. Compared to native ghrelin, hexarelin does not appear to disrupt blood sugar regulation, suggesting a potentially favorable metabolic profile2. Its GH-releasing effects are influenced by age — responses are reduced in older adults but may be partially restored by combining hexarelin with other agents3,12. Research into hexarelin's cardiovascular, metabolic, and bone-related actions is actively developing, with preclinical findings supporting a broad range of biological activities mediated through both classical and novel receptor pathways9,14,15.

This is the layperson summary. Mechanism, dosing, the evidence base, and the published literature are in the sections below — every claim links to its source.

§02In depth

Hexarelin (His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2) is a synthetic hexapeptide growth hormone secretagogue (GHS) that functions as an agonist at the GHS receptor type 1a (GHS-R1a), also known as the ghrelin receptor4,5. The GHS-R1a is a G-protein-coupled receptor expressed predominantly in the hypothalamus and pituitary, where hexarelin binding stimulates GH secretion through a mechanism that involves both direct pituitary somatotroph stimulation and suppression of hypothalamic somatostatin (SS) tone11. Unlike GHRH, which acts solely at the pituitary, hexarelin's mechanism incorporates partial resistance to exogenous somatostatin infusion, and uniquely enhances GH release upon SS withdrawal — an effect not observed with GHRH alone — suggesting hexarelin may also facilitate endogenous GHRH release at the hypothalamic level11. The synergistic GH responses observed when hexarelin is combined with GHRH are consistent with these complementary mechanisms operating at distinct sites3,5.

Hexarelin's GH-releasing activity is additive with exogenous CRH at the HPA level, but not with the AVP analog desmopressin, indicating that its stimulation of ACTH and cortisol secretion is mediated primarily through endogenous arginine vasopressin (AVP) release rather than CRH1. Opiate receptor pathways are not required for hexarelin's GH-releasing effects, as confirmed by naloxone non-interference, though there may be partial convergence between GHS and opioid signaling specifically for HPA axis activation6.

A critical pharmacological distinction of hexarelin from native ghrelin is its lack of metabolic disruption: despite producing comparable GHS-R1a activation and GH secretion, hexarelin does not acutely elevate blood glucose or suppress insulin2, and unlike ghrelin, does not stimulate aldosterone release5. This suggests ghrelin's metabolic and adrenal effects involve receptor subtypes or direct pancreatic/adrenal actions not shared by synthetic GHS peptides.

Hexarelin also interacts with receptor systems beyond GHS-R1a. Radioligand binding studies in human peripheral tissues identified high-affinity hexarelin binding sites in the myocardium, adrenal glands, gonads, arteries, and liver that cannot be displaced by ghrelin or the non-peptidyl GHS MK-0677 — strongly implicating a distinct peptidyl GHS-specific receptor subtype in non-endocrine tissues14. In cardiac tissue, CD36 has been identified as one such alternative binding protein mediating hexarelin's cardiovascular effects; hexarelin activation of CD36 in isolated perfused hearts produced dose-dependent coronary vasoconstriction, an effect absent in CD36-null and CD36-deficient animal models9. In adipocytes, hexarelin inhibits isoproterenol-stimulated lipolysis through a high-affinity non-GHS-R1a binding site16. These peripheral receptor interactions may explain the GH-independent positive inotropic effects observed in human cardiac studies7.

Pharmacokineticaly, peak GH responses occur approximately 30 minutes post-IV injection and return to baseline within 240 minutes, with an estimated serum GH half-life of approximately 55 minutes4. Subcutaneous bioavailability is approximately 77% relative to IV, while intranasal and oral bioavailabilities are approximately 4.8% and 0.3% respectively10.

§04Evidence & efficacy

Evidence base
208Studies
65Human
68Animal

Hexarelin is an efficacious GH secretagogue in humans across multiple well-replicated studies. A clear dose-response relationship has been established for IV administration, with near-maximal GH release achieved at 2 mcg/kg4. Peak GH concentrations of approximately 55 ng/mL following 2 mcg/kg IV represent a roughly 14-fold increase over placebo4, and hexarelin consistently produces greater GH release than equidose GHRH5,10. GH responses are robust and highly reproducible across repeated administrations10, and biologically meaningful GH release has been demonstrated via subcutaneous and oral routes as well10,13.

GH-releasing efficacy is significantly modulated by age — responses are substantially blunted in elderly subjects compared to younger adults3,12 — but may be substantially restored by co-administration with arginine or GHRH3,12, suggesting neuroendocrine regulatory mechanisms rather than receptor-level impairment underlie this age-related difference.

Beyond GH secretion, hexarelin has been reported to improve left ventricular ejection fraction in humans in a GH-independent manner7, stimulate osteoblast proliferation and differentiation markers in preclinical bone models17, and inhibit lipolysis in adipocyte preparations via a novel receptor pathway16. Hexarelin and related GHS compounds have also been shown to inhibit breast carcinoma cell proliferation in vitro15, and hexarelin analogue peptides appear to activate oxytocinergic neuronal pathways linked to sexual function in animal models19.

§05Safety

Hexarelin has demonstrated good general tolerability across multiple human studies at doses ranging from 0.5 to 3.0 mcg/kg administered intravenously, subcutaneously, intranasally, and orally4,10. No serious adverse events have been reported in any of the published abstracts reviewed. The most commonly noted acute observation was a small but statistically significant increase in appetite following IV administration, assessed by visual analog scales1. Hemodynamic parameters including heart rate and mean blood pressure remained stable in a cardiovascular study using IV hexarelin7.

Hexarelin stimulates the hypothalamic-pituitary-adrenal axis, producing measurable elevations in ACTH and cortisol1,6, and also transiently increases prolactin5,6. These hormonal co-activations are relevant for long-term safety considerations, particularly in populations sensitive to cortisol elevation. Unlike native ghrelin, hexarelin does not acutely disrupt glucose homeostasis or suppress insulin secretion in healthy volunteers2, which represents a favorable distinction for metabolic safety.

In preclinical cardiac tissue studies, hexarelin has been shown to produce coronary vasoconstriction via CD36 receptor activation9, and negative inotropic effects on isolated cardiac muscle preparations have been observed with related GHS peptides18. The clinical significance of these findings in intact human cardiovascular physiology is being characterized in ongoing research. Specific binding sites for hexarelin have been identified across a wide range of human peripheral tissues including the myocardium, adrenal glands, gonads, liver, and lungs14, indicating broad systemic receptor engagement beyond the hypothalamo-pituitary axis.

§06History

Hexarelin was developed in the early 1990s by Europeptides (later associated with Deghenghi and collaborators) as part of a program to create synthetic growth hormone-releasing peptides (GHRPs) with improved potency and novel administration routes compared to the first-generation GHRP-6. The compound's hexapeptide sequence (His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2) was designed to optimize GH secretagogue activity while maintaining resistance to peptidase degradation4.

The first pharmacokinetic and dose-response characterization in humans was published in 1994, establishing dose-dependent IV GH release with an ED50 of approximately 0.50–0.64 mcg/kg and demonstrating meaningful activity via subcutaneous, intranasal, and oral routes4,10 — the latter representing a notable advance over earlier peptidyl GHS compounds. Initial studies quickly established hexarelin's superiority over GHRH in GH-releasing potency10, and by the mid-1990s the peptide was being used as a research tool to probe the then-uncharacterized GH secretagogue receptor system6,11.

The 2001 discovery and characterization of ghrelin as the endogenous GHS-R1a ligand transformed understanding of hexarelin's mechanism, with comparative studies confirming shared but non-identical receptor pharmacology between hexarelin and ghrelin2,5. Concurrent work in the early 2000s revealed hexarelin's GH-independent cardiac effects and identified CD36 as a myocardial hexarelin receptor9, opening a distinct cardiovascular research avenue. The identification of GHS binding sites in breast carcinoma tissue15 and osteoblasts17 further expanded the biological landscape for GHS peptides. Today, hexarelin remains an important research compound for investigating GHS receptor biology, neuroendocrine regulation, and cardiac GHS pharmacology.

§07References