Hexarelin: GHRP-Class Hexapeptide Research Overview

Hexarelin (INN: examorelin) is a synthetic hexapeptide growth hormone-releasing peptide (GHRP) with the sequence His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH2. It was developed in the early 1990s and is structurally related to GHRP-6, with modifications that enhance potency. Among research-market GHRPs, hexarelin has one of the more substantial peer-reviewed evidence bases: its GH-releasing activity was characterized in rat and human studies in the mid-1990s, and a series of Italian research publications in the late 1990s and early 2000s documented a surprising and significant cardiac effect — independent of GH secretion — mediated by specific cardiac GH secretagogue receptors. Despite this research, hexarelin has never advanced to regulatory approval for human use in any jurisdiction and is sold as a research peptide.

What Is Hexarelin?

Hexarelin belongs to the GHRP class — synthetic peptide agonists of the ghrelin receptor (GHS-R1a) that stimulate GH release from the pituitary. GHRPs were developed in the 1980s and 1990s as research tools to study GH regulation and as potential therapeutic agents for GH deficiency and related conditions. Hexarelin (six residues, MW ≈887 Da) is a close structural relative of GHRP-6, with modifications at the Trp-2 position (N-methylation) and other residues that increase GH-releasing potency.

Hexarelin is listed in the Pepticker catalog under the alternate name examorelin and is categorized as a GH-secretagogue. It is not FDA-approved, not EMA-approved, not MHRA-approved, and not TGA-approved. Its sale is legal for research purposes in the US, Canada, and UK; it is TGA Schedule 4 restricted in Australia.

Mechanism of Action

Hexarelin acts as a potent agonist of the GHS-R1a receptor (the ghrelin receptor), expressed in the pituitary, hypothalamus, heart, and other tissues. Pituitary GH release: GHS-R1a activation in pituitary somatotrophs stimulates GH secretion via cAMP-independent signaling. Hexarelin is among the most potent GHRPs in terms of pituitary GH release in animal models. GHRH synergism: Hexarelin acts synergistically with endogenous growth hormone-releasing hormone (GHRH), meaning its GH-stimulating effect is amplified in the presence of normal GHRH tone.

Cardiac mechanism (GH-independent): Locatelli et al. (1999) identified a specific cardiac GH secretagogue receptor distinct from pituitary GHS-R1a, characterized by an 84 kDa molecular weight, a Kd of 14.5 nmol/L, and a density of 91 fmol/mg protein in rat cardiac membranes. Activation of this receptor by hexarelin produces positive inotropic and cardioprotective effects that are not mediated by GH — demonstrated by the finding that these effects persist in GH-deficient and hypopituitary animals and humans after hexarelin administration. This GH-independent cardiac mechanism distinguishes hexarelin from classical GH-replacement therapy.

What the Research Shows

GH secretion studies (Imbimbo et al., 1994; Locatelli et al., 1998): The foundational GH-releasing characterization of hexarelin was conducted in the mid-1990s. Locatelli et al. (1994–1998, published in peer-reviewed endocrine journals) established hexarelin's GH-releasing activity in infant and adult rats and in human subjects. These studies demonstrated that hexarelin produces robust, dose-dependent GH release that is among the largest observed with synthetic GHRPs, and that it acts through mechanisms distinct from GHRH.

Cardiac effects in GH-deficient humans (Rahim et al., 1999; PubMed 10528131): Rahim et al. examined the cardiac effects of hexarelin in hypopituitary adults. The study found that hexarelin improved cardiac performance in GH-deficient patients, including increased left ventricular ejection fraction, independently of any GH-mediated mechanism. This was a pivotal finding establishing direct cardiac GH secretagogue receptor activity in humans.

Cardiac effects in coronary artery disease (Bisi et al., 2002; PubMed 12144941): In a study of patients undergoing coronary artery bypass surgery, acute intravenous hexarelin improved cardiac performance without significant changes in systemic vascular resistance, and the effect was not reproduced by GH-releasing hormone or recombinant human GH. This confirmed that hexarelin's cardiotropic effect is mediated by cardiac GHS receptors, not pituitary GH release.

Cardioprotection in ischemia-reperfusion (Rossoni et al., 1999; PubMed 10465272): Animal studies demonstrated that hexarelin reduces postischemic ventricular dysfunction in isolated hearts from GH-deficient and aged rats, further establishing the GH-independent cardiac mechanism. The cardiovascular action of hexarelin in this context was reviewed comprehensively in a 2014 PMC article (PMC4178518).

GH desensitization: One notable pharmacological property of hexarelin that has been characterized in human studies is tachyphylaxis — repeated administration leads to desensitization of the pituitary GH response. This has been observed in several repeated-dosing studies and is more pronounced with hexarelin than with some other GHRPs, limiting its utility for sustained GH elevation.

Pharmacokinetics

Hexarelin pharmacokinetics have been partially characterized in human studies: Half-life: approximately 20–25 minutes plasma elimination half-life following intravenous administration, based on GH response time-course data from human studies. The Pepticker catalog reports approximately 25 minutes for plasma elimination. Onset: GH peak occurs at approximately 15–30 minutes post-administration in human studies, with the cardiotropic effect also peaking at approximately 15–30 minutes in cardiac studies. Molecular weight: 887.03 Da. Administration routes studied: subcutaneous and intravenous administration have been used in published human studies. Intranasal and oral bioavailability are low for this peptide. Metabolism: hepatic and renal proteolysis; metabolites not fully characterized.

Common Research Dose Ranges

Not medical advice. These are ranges reported in research literature, not personalized recommendations. Consult your physician.

Published human studies have used doses of hexarelin in the range of 1–2 mcg/kg administered intravenously or subcutaneously, which for a 70 kg subject corresponds to approximately 70–140 mcg per dose. The cardiac study by Bisi et al. (2002) used 2 mcg/kg IV. These doses produced measurable GH secretion and, where evaluated, cardiac effects. Research-community subcutaneous doses commonly cited are 100–200 mcg per administration, which are in the range of published clinical-study doses. Notably, the GH response desensitizes with repeat dosing — a consideration that is documented in human studies.

Storage and Handling

Hexarelin is sold as a lyophilized powder. Standard handling: store lyophilized powder at −20 °C, protected from light and moisture. Reconstitute with sterile bacteriostatic water; store reconstituted solution at 2–8 °C and use within 28 days. Avoid repeated freeze-thaw cycles. Hexarelin contains a D-amino acid (D-2-methyl-Trp, D-Phe) that confers resistance to some proteases, providing somewhat better inherent stability than all-L-amino acid peptides of similar size.

What Hexarelin Is NOT

Hexarelin is not recombinant human growth hormone (rhGH). It stimulates endogenous GH release via the pituitary; it does not introduce exogenous GH into the body. The cardiotropic effects of hexarelin are not mediated by GH and would not be reproduced by rhGH administration. Hexarelin is not approved by any Western regulatory agency (FDA, EMA, MHRA, TGA) for human use. Despite a meaningful published clinical research record — which is unusual for GHRPs — it did not advance through the regulatory approval process. Hexarelin is not equivalent to other GHRPs in terms of research depth. Ipamorelin, GHRP-2, and GHRP-6 have more modest human-study records; hexarelin's cardiac studies represent a distinct scientific contribution.

References

See citations below. Core references: Locatelli et al. 1994 (GH-releasing activity in rats), Rahim et al. 1999 (cardiac effects in hypopituitary adults), Bisi et al. 2002 (coronary artery disease bypass surgery study), Rossoni et al. 1999 (GH-independent cardioprotection), and the 2014 PMC cardiovascular action review.