Hexarelin Research: Two Receptors, a Cardiac Literature and Documented Desensitisation

What is hexarelin?

What is hexarelin? It is a synthetic hexapeptide with the sequence His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH₂, carrying a C-terminal amide. It appears in the literature as examorelin, and in the supplier trade as hexarelin acetate. The comparison that defines it is structural: hexarelin is GHRP-6 with a methyl group added to the D-tryptophan at position 2. One carbon and two hydrogens — a mass difference of 14 daltons.

That the two compounds have measurably different research profiles despite that near-identity is the interesting part, and it is also a practical warning: no purity percentage on a certificate can distinguish them, only a mass spectrum can. Pharmacologically hexarelin is an agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a), the ghrelin receptor — and, per the work described below, a ligand at CD36 as well. Everything here describes chemistry, receptor pharmacology and published research models.

Discovery and origin in the literature

Hexarelin emerged in the early 1990s from the structure–activity programme that grew out of Bowers’ original hexapeptide work, and it was characterised in humans quickly and unusually thoroughly for a compound of this class. Ghigo and colleagues (1994, J Clin Endocrinol Metab, PMID 8126144) evaluated its growth-hormone-releasing activity in healthy young volunteers across four different administration routes — intravenous, subcutaneous, intranasal and oral — with growth-hormone-releasing hormone as a reference comparator, reporting that the peptide produced measurable release by every route tested. Imbimbo and colleagues ran a formal ascending-dose study in humans in the same year (Eur J Clin Pharmacol, PMID 7957536).

Two things about that early record are worth noting as history. First, the human characterisation came fast and was conducted in an ordinary clinical-pharmacology framework. Second, it went no further: no registered indication, no phase-3 programme, and no approved product containing hexarelin exists anywhere. The compound was investigated seriously and then, in clinical-development terms, stopped.

Reference data

Identity facts from the public chemical record (PubChem CID 6918297) and standard catalogue data. Fields that could not be sourced are omitted rather than estimated.

The two tryptophan-family residues make this a strongly UV-absorbing peptide, convenient for chromatographic detection and, as with GHRP-6, oxidation-sensitive — oxidised species are among the impurities a reversed-phase method is expected to resolve. Molecule and analytical facts only; no reconstitution volume, concentration or route is given or implied.

Mechanisms researchers have examined

The hexarelin mechanism literature has two arms, and keeping them separate is the whole point of reading it carefully:

• GHS-R1a agonism (the pituitary arm) — hexarelin activates the ghrelin receptor in pituitary and hypothalamus, the mechanism shared with GHRP-6, GHRP-2 and ipamorelin, and reviewed for the class by Müller et al. (2015, Mol Metab, PMID 26042199).
• CD36 binding (the cardiac arm) — Bodart et al. (2002, Circ Res, PMID 11988484) labelled rat cardiac membranes with a radioactive photoactivatable hexarelin derivative and purified the binding protein it captured. The N-terminal sequence of the deglycosylated protein was identical to rat CD36, a multifunctional glycoprotein expressed in cardiomyocytes and microvascular endothelial cells. This is a distinct molecular target, identified by direct biochemical means rather than inferred.
• Effects that survive removal of the GH axis — Locatelli et al. (1999, Endocrinology, PMID 10465272) tested hexarelin in hypophysectomised rats, an experimental design chosen specifically so that any effect could not be growth-hormone-mediated. A comparator secretagogue that does not bind the heart was ineffective in the same model. That contrast is the mechanistic evidence for a genuinely GH-independent cardiac action.
• Response attenuation on repeated exposure — described in the human findings below; it is a pharmacodynamic property of the compound rather than a study artefact, and it is reported in the literature as partial and reversible.

Research findings by area

The cardiac literature, and why it does not point one way

This is the section most likely to be quoted selectively elsewhere, so it is worth setting out in full. Locatelli et al. (1999) reported that hexarelin given to hypophysectomised rats prevented exacerbation of ischaemia-reperfusion damage, with effects on left ventricular end-diastolic pressure, creatine kinase release into the perfusate and recovery of contractility, concluding the action was not mediated by growth hormone. McDonald et al. (2020, Biomed Pharmacother, PMID 32403043) examined neuroinflammatory pathways in a mouse myocardial ischaemia-reperfusion model. Marleau et al. (2006, Cardiovasc Res, PMID 16219302) reviewed the cardiac and peripheral actions of growth hormone and its releasing peptides.

Set against that, the same CD36 work that established the cardiac target reported something else: in perfused hearts, activation of CD36 by hexarelin increased coronary perfusion pressure — a vasoconstrictive response — and the effect was absent in hearts from CD36-null mice and from rats genetically deficient in CD36. The authors’ own closing suggestion was that CD36 may mediate the coronary vasospasm seen in hypercholesterolaemia and atherosclerosis. Reported accurately, then, the CD36 arm is not a story about a protective compound; it is a story about a molecular target whose activation does different things in different models. All of the above are animal studies, and animal findings cannot establish outcomes in people. This page draws no conclusion and makes no claim about cardiac effects.

What sixteen weeks of human exposure showed

Rahim, O’Neill and Shalet (1998, J Clin Endocrinol Metab, PMID 9589671) conducted the longest published human administration study in this compound cluster: twice-daily subcutaneous hexarelin over sixteen weeks in adults, with the growth-hormone response to a challenge measured at intervals and again four weeks after stopping. The area under the growth-hormone curve fell significantly by week 4 and further by week 16, then rose again four weeks after cessation to a level not significantly different from baseline. The authors summarised this as a partial and reversible attenuation of the growth-hormone response.

The rest of what they measured is equally worth stating. Serum IGF-1 and IGFBP-3 did not change significantly over the twenty-week period. Of the bone markers assessed, only C-terminal propeptide of type I collagen changed significantly. Total body fat, lean body mass and bone mineral density had not changed significantly at week 16 compared with baseline. The authors’ own conclusion was that the biological impact of this schedule on the GH–IGF-1 axis appeared minimal and that the therapeutic potential of chronic hexarelin required further investigation. That is the study’s finding, reported as the paper reports it, and it is the single most informative human dataset available on this compound.

Research models and evidence status

Hexarelin has a genuine and interesting mechanistic literature — two identified molecular targets, a well-designed hypophysectomy experiment, and early human pharmacology across multiple routes. What it does not have is a completed development programme or a body of outcome evidence.

What is not established

No approved product contains hexarelin and it holds no registered indication anywhere. The cardiac work is animal work, and it includes a published vasoconstrictive finding alongside the protective ones; it does not establish a cardiac benefit in people and nothing here suggests it does. The one long human study reported the growth-hormone response attenuating, IGF-1 and IGFBP-3 unchanged, and body composition and bone mineral density unchanged at sixteen weeks — a set of null results that vendor pages for this compound rarely mention. No long-term safety data exist for use in healthy people. Where the honest summary of a compound is “mechanistically interesting, clinically undeveloped,” that is what this page says.

On anti-doping status, reported as fact and not as a use case: growth-hormone secretagogues, hexarelin included, appear under section S2 of the World Anti-Doping Agency Prohibited List and are prohibited at all times, in and out of competition.

Hexarelin among the ghrelin-receptor agonists

Within the GHS-R1a family the honest differentiators are selectivity and off-target activity, not potency league tables. GHRP-6 is the original, least selective member, with a rodent appetite and adiposity literature. GHRP-2 is the one that became a pituitary-function test agent and whose ACTH response is used diagnostically. Ipamorelin is the member characterised as selective — its page covers that, and it is not restated here. MK-677 reaches the same receptor without being a peptide at all. Hexarelin’s distinguishing feature is the second target: CD36 gives it a mechanism the others do not share, and that is why its literature drifts into cardiology journals rather than endocrinology ones.

Across the receptor divide sit the GHRH analogues — sermorelin, CJC-1295 and tesamorelin — acting at an entirely different receptor. Receptor-family context only; nothing here is a protocol, a stack or a recommendation.

How to verify this compound yourself

Identity and purity rest on two orthogonal methods, both reported on the per-batch Certificate of Analysis — and for hexarelin the identity half carries unusual weight:

• Mass-spec identity — the measured mass is checked against the expected ≈ 887 Da. Hexarelin and GHRP-6 differ by exactly one methyl group, 14 Da. A vial of GHRP-6 sold as hexarelin would be chemically pure, correctly lyophilized and completely wrong, and only a mass spectrum would show it. This is the check that matters most on this compound.
• HPLC purity — reversed-phase chromatography separates the target from synthesis-related impurities and reports purity as a percentage of the chromatogram, covering deletion sequences, diastereomers from the D-configured positions, and oxidised tryptophan species.
• Endotoxin and sterility — where tested, separate quality attributes reported in EU/mg or as a sterility result, independent of chemical purity.

See how to read a COA for what each line on a certificate means, how to verify peptide purity for how the two methods fit together, and the self-serve verify tool to check the exact batch on a vial in hand.

Research-grade sourcing and verification

For laboratory research use only. Hexarelin is not held in stock; it is listed as available to order in the sourcing catalogue, with a typical lead time of two to three weeks and a quote on request. Material supplied ships with a per-batch Certificate of Analysis reporting HPLC purity (%) and mass-spec identity confirmation at the lot level — which, on a compound separated from its nearest relative by fourteen daltons, is the difference between documentation and assumption. Sourcing and identity-assurance framing only.

Frequently asked questions

Literature cited

1. Ghigo E, Arvat E, Gianotti L, Imbimbo BP, Lenaerts V, Deghenghi R, Camanni F. “Growth hormone-releasing activity of hexarelin, a new synthetic hexapeptide, after intravenous, subcutaneous, intranasal, and oral administration in man.” J Clin Endocrinol Metab. 1994;78(3):693–698. PMID 8126144. pubmed.ncbi.nlm.nih.gov/8126144.
2. Imbimbo BP, Mant T, Edwards M, et al. “Growth hormone-releasing activity of hexarelin in humans. A dose-response study.” Eur J Clin Pharmacol. 1994;46(5):421–425. PMID 7957536. pubmed.ncbi.nlm.nih.gov/7957536.
3. Rahim A, O’Neill PA, Shalet SM. “Growth hormone status during long-term hexarelin therapy.” J Clin Endocrinol Metab. 1998;83(5):1644–1649. PMID 9589671. pubmed.ncbi.nlm.nih.gov/9589671.
4. Locatelli V, Rossoni G, Schweiger F, et al. “Growth hormone-independent cardioprotective effects of hexarelin in the rat.” Endocrinology. 1999;140(9):4024–4031. PMID 10465272. pubmed.ncbi.nlm.nih.gov/10465272.
5. Bodart V, Febbraio M, Demers A, et al. “CD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart.” Circ Res. 2002;90(8):844–849. PMID 11988484. pubmed.ncbi.nlm.nih.gov/11988484.
6. Marleau S, Mulumba M, Lamontagne D, Ong H. “Cardiac and peripheral actions of growth hormone and its releasing peptides: relevance for the treatment of cardiomyopathies.” Cardiovasc Res. 2006;69(1):26–35. PMID 16219302. pubmed.ncbi.nlm.nih.gov/16219302.
7. McDonald H, Peart J, Kurniawan ND, et al. “Hexarelin targets neuroinflammatory pathways to preserve cardiac morphology and function in a mouse model of myocardial ischemia-reperfusion.” Biomed Pharmacother. 2020;127:110165. PMID 32403043. pubmed.ncbi.nlm.nih.gov/32403043.
8. Müller TD, Nogueiras R, Andermann ML, et al. “Ghrelin.” Mol Metab. 2015;4(6):437–460. PMID 26042199. pubmed.ncbi.nlm.nih.gov/26042199.
9. National Center for Biotechnology Information. “PubChem Compound Summary for CID 6918297, Hexarelin.” pubchem.ncbi.nlm.nih.gov/compound/6918297 (formula, mass, CAS 140703-51-1).
10. World Anti-Doping Agency. “The Prohibited List” — section S2, Peptide Hormones, Growth Factors, Related Substances and Mimetics. wada-ama.org/en/prohibited-list.