# Hexarelin: Structure, GHS-R1a and CD36 Targets, and the Research Record > A laboratory reference to hexarelin — the stabilised GHRP-6 analogue whose second target, the cardiac scavenger receptor CD36, makes it a useful pharmacological probe. Web page: https://peptidemedixeu.com/en/learn/what-is-hexarelin/ · Peptide Medix EU · 7 min read · Updated: 2026-01-26 A synthetic hexapeptide with the sequence His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2, hexarelin was designed as a metabolically stabilised version of [GHRP-6](https://peptidemedixeu.com/en/products/ghrp-6/) and has been studied both as an agonist at the growth hormone secretagogue receptor (GHS-R1a) and as a ligand for the cardiac scavenger receptor CD36. This dual-target character sets it apart within the secretagogue literature: a large share of the published work concerns cardiovascular models in which growth hormone release cannot explain what was measured. Peptide Medix EU stocks hexarelin as a lyophilized powder in sealed 2 mg and 5 mg vials, within the GHRPs and secretagogues range. It is sold purely as a research [compound for in-vitro](https://peptidemedixeu.com/en/glossary/in-vitro/) and preclinical laboratory use. ## Defining hexarelin Hexarelin is a synthetic hexapeptide, catalogued elsewhere as examorelin and EP-23905. It sits in the [GHRP family](https://peptidemedixeu.com/en/glossary/ghrp/) — short peptides that drive pituitary somatotrophs through the ghrelin receptor (GHS-R1a) instead of the GHRH receptor. Chemically it is a compact, wholly synthetic molecule: formula C47H58N12O6, mass 887.04 g/mol, CAS 140703-51-1, ending in a C-terminal amide. In practice [hexarelin serves](https://peptidemedixeu.com/en/products/hexarelin/) as a reference agonist. When a study needs a thoroughly characterised, high-efficacy GHS-R1a ligand to benchmark a newer secretagogue against, it is one of the compounds the literature turns to, together with GHRP-2 and ipamorelin. ## Where the molecule came from, and how it is built The GHRP series grew out of Cyril Bowers's enkephalin-derived research in the 1970s and 1980s, which yielded GHRP-6. Romano Deghenghi and co-workers then developed hexarelin from that scaffold in the early 1990s. One methyl group separates the two peptides: position 2 holds D-tryptophan in GHRP-6 and 2-methyl-D-tryptophan in hexarelin. The substitution is textbook peptide stabilisation. Extra steric bulk next to the indole ring has been reported to slow enzymatic breakdown and increase receptor potency, while the D-amino acids already present at positions 2 and 5 shield the backbone from the aminopeptidases that would otherwise clear an all-L hexapeptide quickly. Capping the C-terminus as an amide removes the free carboxylate — another stability feature common to the GHRP family. Structurally hexarelin looks nothing like growth hormone and shares no meaningful homology with GHRH. Rather than being a fragment of a human hormone, it is a peptidomimetic of the active core of ghrelin, which is why the GHRP class is described as a family of synthetic secretagogues rather than as analogues. ## Reported mechanisms Hexarelin's principal reported mechanism is agonism at GHS-R1a, a G-protein-coupled receptor present on pituitary somatotrophs and in the hypothalamic arcuate nucleus. Occupancy couples to Gq and phospholipase C, generating inositol trisphosphate and raising intracellular calcium, which in pituitary preparations accompanies release of secretory granules. The literature also reports a permissive interplay with endogenous GHRH tone and partial functional antagonism of somatostatin, so in intact animals the size of the response depends on the hypothalamic state at the moment of administration rather than on the peptide by itself. The second and more unusual limb of the mechanism involves CD36. Hexarelin was found to bind this scavenger receptor in cardiac membrane preparations, and CD36 is expressed in cardiomyocytes, macrophages and endothelium. As CD36 has nothing to do with growth hormone signalling, effects seen in cardiac models — including work in hypophysectomised or GH-deficient animals — are usually ascribed to this route rather than to the somatotropic axis. One reason investigators reach for hexarelin is precisely to use it as a probe that separates the two. A third mechanistic trait recurs throughout the GHRP literature: receptor desensitisation. Sustained or closely spaced exposure blunts the secretory response in a way that pulsatile exposure does not, an effect attributed to internalisation of GHS-R1a. Any design that uses hexarelin across more than one time point must take this into account. ## What has been studied ### Growth hormone and the IGF-1 axis Pituitary studies in rodents and cell systems from the 1990s onwards described hexarelin as one of the more potent secretagogues of its era, giving larger GH release than GHRP-6 in head-to-head comparisons. Human pharmacology studies carried out during clinical development reported GH release after intravenous, [subcutaneous administration](https://peptidemedixeu.com/en/glossary/subcutaneous/), intranasal and oral dosing, with bioavailability falling progressively across those routes. The programme never reached approval and no marketed product exists. Some of that work measured downstream IGF-1 responses as a secondary endpoint. ### Cardiac and vascular models Cardiovascular research is why hexarelin is still used as a laboratory tool. Rodent studies in ischaemia–reperfusion and post-infarction models reported shifts in cardiac contractile parameters and in markers of cardiomyocyte survival, and similar observations in GH-deficient animals pointed to a route independent of growth hormone. Binding work later identified CD36 as the target involved. All of this is preclinical: the endpoints are haemodynamic and histological measurements in animals, not clinical outcomes. ### Selectivity and off-target hormone release Hexarelin, unlike ipamorelin, is not a selective secretagogue. Human and animal studies have reported cortisol, ACTH and prolactin rising alongside GH, which matters whenever a design calls for a clean GH signal. That contrast is the practical reason to choose one compound over the other and is examined closely in our hexarelin [versus ipamorelin](https://peptidemedixeu.com/en/products/ipamorelin/) comparison. ### Skeletal muscle and metabolic models A smaller body of preclinical work has looked at hexarelin in muscle-wasting and cachexia models and in adipose tissue preparations, usually as one strand of a wider investigation of ghrelin-receptor pharmacology. These remain exploratory animal and cell-culture observations rather than settled findings. ## Vial sizes available The 2 mg vial fits short in-vitro series and receptor assays, while the 5 mg vial is the better value where a laboratory prepares repeatedly from one lot and wants to avoid changing lots midway through a study. Purchasing points are treated separately in our hexarelin buying guide. ## Reconstitution and storage for laboratory work Hexarelin arrives as a lyophilized cake and is made up with [bacteriostatic water where multiple draws](https://peptidemedixeu.com/en/products/bacteriostatic-water/) are planned, or with sterile water if a preservative would interfere with the assay. Direct the solvent down the wall of the vial rather than onto the cake, and swirl instead of shaking; this small hexapeptide dissolves easily, and vigorous shaking mostly creates foam that makes accurate withdrawal harder. Working out the concentration is routine arithmetic. Reconstituting a 5 mg vial with 2 mL of diluent gives 2.5 mg/mL, or 2,500 mcg/mL, so 0.1 mL — the 10-unit mark on a U-100 syringe — holds 250 mcg of peptide. Using 5 mL on the same vial gives 1 mg/mL and 100 mcg per 0.1 mL. Our reconstitution guide describes the full procedure, and reconstitution math explained covers the calculations. Store sealed lyophilized vials at −20 °C, protected from light and moisture. Keep reconstituted material at 2–8 °C and use it within the study window; when a series will span weeks, dividing it into [sterile empty vials](https://peptidemedixeu.com/en/products/sterile-empty-vials/) and freezing the aliquots avoids repeatedly freezing and thawing one stock. How to store peptides summarises general practice. ## Purity, the COA and how to read it Each hexarelin lot comes with a certificate of analysis tied to the lot number printed on the vial. The two most informative entries are the HPLC chromatogram, which expresses purity as the main peak's proportion of total peak area, and the mass spectrometry result, which verifies identity against the expected 887.04 g/mol. Purity over 99% together with an [observed mass value](https://peptidemedixeu.com/en/learn/mass-spectrometry-peptide-identity/) matching theory within instrument tolerance indicates that the vial holds the intended molecule and very little else. Two compound-specific details deserve attention. First, the mass spectrum should fit the 2-methyl-tryptophan analogue rather than GHRP-6, because only 14 Da separate them — easily overlooked in a hurried reading. Second, the counter-ion should be declared: peptides purified by reversed-phase chromatography generally come as TFA salts, and the salt content changes how much peptide the vial actually holds. Our guide to reading a peptide COA goes through a complete certificate line by line. ## Regulatory position Hexarelin carries no marketing authorisation in the United States or anywhere else. Its 1990s clinical programme produced no approved product, so there is neither a reference-listed medicine nor approved labelling. It is additionally banned in sport under anti-doping rules covering growth hormone secretagogues. ## Related peptides and further reading Elsewhere in the same receptor family, ipamorelin is the selective option, GHRP-2 the potency-oriented one, and GHRP-6 the parent scaffold from which hexarelin was derived. Researchers combining a secretagogue with a compound acting on the GHRH side usually look to the GHRH analogue range. For wider context on how these classes relate, see our muscle growth research overview and the pituitary and hypothalamus research hub. ## Frequently asked questions ### What role does hexarelin play in research? Laboratories use it as a benchmark growth hormone secretagogue in pituitary and receptor pharmacology, and as a probe in cardiac studies: because it also binds the scavenger receptor CD36, investigators can tell GHS-R1a-dependent findings apart from GHS-R1a-independent ones. The entire published record is in-vitro or preclinical. ### What separates hexarelin from GHRP-6? A single methyl group. Where GHRP-6 carries D-tryptophan at position 2, hexarelin carries 2-methyl-D-tryptophan, a change reported to reduce enzymatic clearance and to raise potency at GHS-R1a. The resulting 14 Da gap between the two molecules is something to keep in mind when confirming identity by mass spectrometry. ### Does hexarelin release growth hormone selectively? It does not. Animal and human pharmacology studies described simultaneous rises in cortisol, ACTH and prolactin alongside GH. Within this family, ipamorelin is the selective member; hexarelin is not, and that has to be weighed when an experiment requires an isolated GH signal. ### What is the significance of CD36? Binding experiments using cardiac membrane preparations pinpointed CD36 — a scavenger receptor found in cardiomyocytes and endothelium — as hexarelin's second target. Where GH-deficient animal models produced effects that growth hormone release could not explain, the literature generally credits this pathway. ### Which molecular weight should appear on the certificate? The free peptide is 887.04 g/mol, with formula C47H58N12O6 and CAS 140703-51-1. The mass spectrometry trace should report an observed mass matching that figure within instrument tolerance, and the certificate should name the counter-ion as well, since reversed-phase purification normally leaves a TFA salt. ### What are the storage requirements in a laboratory? Keep sealed lyophilized vials at −20 °C, shielded from light and moisture. After reconstitution, hold material at 2–8 °C and use it within the planned study period; for longer programmes, transferring aliquots into sterile empty vials and freezing them prevents one stock from being frozen and thawed repeatedly. ### Has hexarelin ever been approved as a medicine? No. The clinical programme run during the 1990s never produced an approved product in any jurisdiction, so neither a reference-listed medicine nor approved labelling exists. What we supply is intended for laboratory investigation only. ## Related products - [Hexarelin](https://peptidemedixeu.com/en/products/hexarelin/): from €38 --- For laboratory research use only. This page is provided for scientific and educational information. Materials referenced here are sold strictly for in-vitro laboratory research by qualified professionals — not for human or veterinary use, and nothing on this page is medical advice.