Hexarelin — identity, handling and published literature

Hexarelin (INN: examorelin) is a synthetic six-residue growth hormone secretagogue peptide of the growth hormone-releasing peptide (GHRP) family, supplied as a sterile lyophilised powder for reconstitution.

NovoVita does not supply hexarelin. This entry exists because the library documents the growth hormone secretagogue field as published, not the catalogue.

Presentation and physical properties

Hexarelin is a C-terminally amidated hexapeptide with the sequence His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH₂. It is a structural analogue of GHRP-6, from which it differs by a single methyl group on the indole ring of the second residue; that residue is the D-enantiomer of 2-methyltryptophan, frequently abbreviated D-Mrp. Two further residues carry the D-configuration and non-proteinogenic modification pattern typical of this peptide class, which is a deliberate feature of the design rather than an impurity signature.

The material is normally presented as a white to off-white lyophilised cake or powder, prepared as the acetate salt in most research-grade preparations. The free-base molecular weight is 887.0 g/mol; a salt-form preparation will assay lower on a peptide-content basis than its gross mass suggests, and the difference between gross vial mass and net peptide content is the most common source of arithmetic error when handling any lyophilised peptide.

The peptide is hydrophilic and freely soluble in water and in aqueous buffers. The molecule carries a basic imidazole side chain (histidine) and a basic primary amine (lysine), with no acidic residues, so the net charge is positive across the physiological pH range. It has no cysteine residues and therefore forms no disulfide bridges, which removes one common degradation and misfolding pathway found in larger peptides.

Reconstitution arithmetic

Hexarelin is not a NovoVita product and therefore has no house vial strength. The arithmetic below is worked for two nominal quantities commonly encountered in research-grade lyophilised presentations. It is unit conversion only: it establishes what concentration results from adding a given volume of diluent to a given mass of peptide, and nothing further.

The relationship is linear. Concentration in mg/mL equals the net peptide mass in the vial divided by the volume of diluent added. Adding diluent to a lyophilised cake produces a solution whose final volume is, for practical purposes at these quantities, equal to the diluent volume added; the displaced volume of the solid is negligible at the milligram scale.

Two arithmetic cautions apply generally. First, a vial labelled by peptide content and a vial labelled by gross salt mass do not contain the same amount of peptide, and the certificate of analysis is the only thing that settles which convention a given preparation uses. Second, the third row of each block is a recurring decimal; carrying it as 0.67 or 1.67 rather than the full value introduces a rounding error of a few tenths of a per cent, which matters only when concentrations from separate preparations are being compared against one another.

Storage and stability

The lyophilised solid is the stable form. Standard laboratory practice for peptides of this class is storage of the sealed lyophilised vial at −20 °C or below, desiccated and protected from light, with the material allowed to reach room temperature before the vial is opened so that atmospheric moisture does not condense onto the cold cake. Lyophilised peptides are hygroscopic, and absorbed water is the principal route by which a dry preparation begins to degrade.

Hexarelin contains two indole side chains — tryptophan at position four and 2-methyltryptophan at position two. Indole is among the more readily oxidised and more photolabile of the amino acid side chains, so light exclusion is a substantive stability measure for this particular sequence rather than a generic precaution. The molecule contains no methionine and no cysteine, so the two other common oxidative degradation routes do not apply.

In solution, peptides of this class are markedly less stable than in the dry state, and solutions are conventionally held refrigerated and used over a short working period. Repeated freeze–thaw cycling of an aqueous solution is avoided as a matter of routine practice; where a solution must be held frozen, it is aliquoted first so that each aliquot is thawed once. No published stability dataset specific to hexarelin in reconstituted solution was identified during the preparation of this entry, so no shelf-life figure is stated here; the absence of that data is itself the relevant fact.

Analytical identity

The compound is registered under CAS 140703-51-1 and PubChem CID 6918297, with molecular formula C₄₇H₅₈N₁₂O₆. The average molecular weight is 887.0 g/mol and the monoisotopic mass is 886.4602 Da.

The single most useful analytical discriminator for this compound is its relationship to GHRP-6. The two peptides share an identical residue sequence and differ only by the 2-methyl substitution on the indole of residue two, giving hexarelin a formula of C₄₇H₅₈N₁₂O₆ against C₄₆H₅₆N₁₂O₆ for GHRP-6 — a difference of exactly one CH₂ unit, or 14.02 Da. A mass measurement alone therefore separates the two cleanly, but a sequence-level method that does not resolve the methylated residue will not.

By electrospray ionisation the peptide is commonly observed as the doubly protonated ion at m/z 444.24 and the singly protonated ion at m/z 887.47, the two basic residues favouring the doubly charged species. The C-terminal amide is a specification point in its own right: hydrolysis of the amide to the free acid raises the monoisotopic mass by approximately 0.98 Da, so a free-acid impurity sits within one mass unit of the parent and requires adequate resolving power to detect. Reversed-phase HPLC with ultraviolet detection at 280 nm is the conventional purity method, the two indole side chains and the phenylalanine giving strong absorbance at that wavelength.

What the published literature investigated

A PubMed search on the term “hexarelin” returns several hundred indexed records. The literature is unusual for a compound of this class in that a substantial proportion of it is human, and the human work is contemporaneous with the compound’s formal pharmaceutical development rather than retrospective.

In vitro studies

Ong and colleagues used a photoactivatable derivative of hexarelin to label binding proteins in anterior pituitary membranes from human, bovine and porcine tissue, and reported identification of a protein of approximately 57 kDa which they characterised as distinct from the previously cloned growth hormone secretagogue receptor [5].

Meanti and colleagues reported that hexarelin and the secretagogue JMV2894 reduced hydrogen peroxide-induced cytotoxicity in a human neuroblastoma SH-SY5Y cell line expressing the mutated SOD1-G93A protein, with the authors attributing the observation to modulation of apoptotic and survival signalling over a 24-hour exposure [14].

Rodent studies

Bodart and colleagues reported that radiolabelled hexarelin bound an 84 kDa cardiac membrane protein which they identified as CD36, and that the coronary perfusion pressure response to hexarelin in perfused hearts was absent in CD36-deficient hearts. The authors framed this as a scavenger-receptor-mediated action distinct from the growth hormone secretagogue receptor, and noted its possible relevance to coronary vasospasm in atherosclerotic disease [10].

Huang and colleagues studied male Sprague-Dawley rats subjected to coronary artery ligation followed by reperfusion, and reported that hexarelin administration was associated with down-regulation of IL-1β and up-regulation of IL-1Ra expression in ischaemic myocardium, assessed by echocardiography, histochemistry and Western blot [12].

Human trials

Human trials of hexarelin itself exist and are numerous. This is a compound with a genuine human evidence base, not a compound whose entry rests on studies of a related molecule.

Imbimbo and colleagues conducted a randomised, double-blind, placebo-controlled rising-dose study in twelve healthy adult male volunteers, reporting dose-dependent increases in plasma growth hormone that peaked at approximately 30 minutes and returned to baseline within 240 minutes [1].

Giustina and colleagues compared growth hormone-releasing hormone, hexarelin and their combination in a randomised crossover design in eight patients with glucocorticoid excess and six matched control subjects [2].

Frenkel and colleagues reported a short preliminary study of intranasal hexarelin over seven days in children of short stature with normal growth hormone secretion, measuring IGF-I, alkaline phosphatase and thyroid stimulating hormone before and after [3]. Ghigo and colleagues subsequently examined whether responsiveness was maintained across repeated intranasal and oral administration in elderly subjects, reporting that short-term administration did not desensitise the growth hormone response [4].

Rahim, O’Neill and Shalet conducted the longest published exposure identified: a 16-week repeated-administration study in healthy elderly subjects, with the growth hormone response measured at baseline and at weeks 1, 4 and 16, and again four weeks after cessation. They reported that the response declined significantly by weeks 4 and 16, recovered after treatment stopped, and concluded that attenuation was partial and reversible. They also reported that IGF-I, IGF binding protein-3 and bone mineral density were essentially unchanged over the period [6].

Korbonits and colleagues studied fifteen healthy young male volunteers in a double-blind design testing hexarelin alone and in combination with corticotropin-releasing hormone and with an arginine vasopressin analogue, concluding that the effect of hexarelin on the hypothalamo-pituitary-adrenal axis did not involve CRH but might occur through stimulation of vasopressin release [7]. Frieboes and colleagues studied seven young healthy male volunteers with simultaneous sleep electroencephalography and nocturnal hormone profiling, reporting decreased slow-wave sleep and reduced EEG delta activity alongside elevated growth hormone and prolactin across the night and elevated ACTH and cortisol during early sleep [11].

Two studies addressed cardiac observations. Bisi and colleagues assessed seven adult male patients with growth hormone deficiency and nine healthy male controls by equilibrium radionuclide angiocardiography, reporting a short-lasting positive inotropic effect without change in catecholamine levels, blood pressure or cardiac output, and concluding that the effect appeared independent of the growth hormone rise [8]. Broglio and colleagues extended this across three groups — seven normal adults, seven growth hormone-deficient patients and twelve patients with severe dilated cardiomyopathy — measuring left ventricular ejection fraction at intervals over an hour, and reported no correlation between ejection fraction change and growth hormone response [9].

Reviews

Sigalos and Pastuszak reviewed the growth hormone secretagogue class, including hexarelin, and characterised the class as promoting pulsatile growth hormone release subject to negative feedback [13].

Evidence gaps and limitations

Hexarelin was developed by Mediolanum Farmaceutici under the codes EP-23905 and MF-6003. It reached phase II and was never marketed. Development did not continue, and no phase III programme was completed for any indication. Everything below follows from that.

There is no efficacy conclusion available from this literature, because no adequately powered trial with a clinical endpoint was ever conducted. The human studies are endocrine-challenge and mechanistic designs, and they are small: the individual studies cited here enrolled between six and twenty-six subjects. The bulk of the human work dates from 1994 to 2004, predating current trial reporting standards, and much of it was conducted by a small number of collaborating groups with involvement from the developer.

There is no long-term safety dataset. The longest published exposure identified is sixteen weeks [6]. Nothing addresses exposure beyond that, and there is no pharmacovigilance system covering a compound that was never marketed.

Off-target endocrine activity is documented rather than hypothetical. Hexarelin was reported to raise ACTH, cortisol and prolactin as well as growth hormone [7][11], and one study reported alteration of sleep architecture [11]. These are not incidental observations; they were the primary endpoints of the studies that found them.

The same reservation applies to the cardiac literature, which is frequently summarised in one direction only. The rodent CD36 work reported coronary vasoconstriction and was framed by its authors as relevant to coronary vasospasm [10], while a separate rodent study reported an anti-inflammatory signalling profile after ischaemia-reperfusion [12]. The human cardiac observations are acute, single-occasion measurements in small groups [8][9]. No outcome trial exists in either direction.

Attenuation of the growth hormone response over repeated administration is a documented finding of the longest study [6], which also reported that IGF-I and bone mineral density did not change measurably over the period. That is a null result on the downstream axis, and it should not be reported as anything else.

Finally, nothing in this literature addresses material of unverified provenance. Every study cited used pharmaceutical-grade compound of known composition prepared under a development programme. The literature says nothing about, and cannot be extended to, preparations of unknown identity or purity.

Regulatory and standards position

United Kingdom. Hexarelin holds no marketing authorisation from the MHRA and is not an authorised medicinal product in the United Kingdom. It is not a controlled drug: it is not scheduled under the Misuse of Drugs Act 1971 or the Misuse of Drugs Regulations 2001. Its lawful status is that of a laboratory chemical. Under MHRA Guidance Note 8 and the doctrine of a medicinal product by presentation, a claim rather than the molecule determines whether a product falls within medicines regulation, so any statement presenting hexarelin as capable of treating, preventing or modifying a condition would bring it within that regime irrespective of how it is labelled.

European Union. There is no European Medicines Agency authorisation for hexarelin and no national authorisation identified in any member state.

United States. Hexarelin is not approved by the FDA for any indication and is not the subject of an approved new drug application. It is not a controlled substance under the Controlled Substances Act. The FDA has issued warning letters to a number of vendors supplying research peptides, taking the position that “research use only” labelling does not determine intended use where other evidence establishes that products are intended for human use; no warning letter naming hexarelin specifically was identified during the preparation of this entry, and none is asserted here.

Anti-doping. Hexarelin is explicitly named on the WADA Prohibited List. It appears under S2.2.4, Growth hormone releasing factors, within the sub-list of GH-releasing peptides (GHRPs), where it is given as “examorelin (hexarelin)” alongside alexamorelin, GHRP-1, GHRP-2 (pralmorelin), GHRP-3, GHRP-4, GHRP-5 and GHRP-6. Class S2 is prohibited at all times, in and out of competition, and substances in the class are non-Specified Substances — the category attracting no reduction in sanction on the basis of inadvertent use. Peptides of this class are within the routine screening scope of WADA-accredited laboratories.

Laboratory handling and safety

Hexarelin is handled as a research chemical of incompletely characterised toxicology. No occupational exposure limit has been established for it, and no comprehensive toxicological dataset exists — an unavoidable consequence of a development programme that stopped at phase II.

General practice for lyophilised peptides applies. The dry powder is readily aerosolised, so the vial is opened and reconstituted with appropriate containment and the operator wears gloves, eye protection and a laboratory coat. Diluent is introduced against the vial wall rather than directly onto the cake, and the vial is swirled rather than shaken; vigorous agitation promotes foaming and surface denaturation without accelerating dissolution.

Because the material is presented sterile and lyophilised, aseptic technique is used at reconstitution regardless of the intended downstream application, on the ordinary basis that a compromised preparation cannot be recovered and cannot be distinguished by inspection. Reconstituted solutions are labelled with the peptide identity, the concentration as calculated, the diluent used and the date of reconstitution — the concentration in particular, since it is not recoverable from the vial after the fact.

Waste is disposed of as laboratory chemical waste in accordance with local arrangements and, in the United Kingdom, with the Control of Substances Hazardous to Health Regulations 2002. A COSHH assessment should be in place before the material is handled. The relevant safety data sheet for the specific preparation in use is the controlling document and takes precedence over this entry.

References

1. Imbimbo BP, Mant T, Edwards M, Amin D, Dalton N, Boutignon F, Lenaerts V, Wüthrich P, Deghenghi R. Growth hormone-releasing activity of hexarelin in humans. A dose-response study. European Journal of Clinical Pharmacology, 1994; 46(5):421–425. Model: human trial. PMID 7957536
2. Giustina A, Bussi AR, Deghenghi R, Imbimbo B, Licini M, Poiesi C, Wehrenberg WB. Comparison of the effects of growth hormone-releasing hormone and hexarelin, a novel growth hormone-releasing peptide-6 analog, on growth hormone secretion in humans with or without glucocorticoid excess. Journal of Endocrinology, 1995; 146(2):227–232. Model: human trial. PMID 7561633
3. Frenkel J, Silbergeld A, Deghenghi R, Laron Z. Short term effect of intranasal administration of hexarelin — a synthetic growth hormone-releasing peptide. Preliminary communication. Journal of Pediatric Endocrinology and Metabolism, 1995; 8(1):43–45. Model: human trial. PMID 7584696
4. Ghigo E, Arvat E, Gianotti L, Grottoli S, Rizzi G, Ceda GP, Boghen MF, Deghenghi R, Camanni F. Short-term administration of intranasal or oral Hexarelin, a synthetic hexapeptide, does not desensitize the growth hormone responsiveness in human aging. European Journal of Endocrinology, 1996; 135(4):407–412. Model: human trial. PMID 8921821
5. Ong H, McNicoll N, Escher E, Collu R, Deghenghi R, Locatelli V, Ghigo E, Muccioli G, Boghen M, Nilsson M. Identification of a pituitary growth hormone-releasing peptide (GHRP) receptor subtype by photoaffinity labeling. Endocrinology, 1998; 139(1):432–435. Model: in vitro. PMID 9421445
6. Rahim A, O’Neill PA, Shalet SM. Growth hormone status during long-term hexarelin therapy. Journal of Clinical Endocrinology and Metabolism, 1998; 83(5):1644–1649. Model: human trial. PMID 9589671
7. Korbonits M, Kaltsas G, Perry LA, Putignano P, Grossman AB, Besser GM, Trainer PJ. The growth hormone secretagogue hexarelin stimulates the hypothalamo-pituitary-adrenal axis via arginine vasopressin. Journal of Clinical Endocrinology and Metabolism, 1999; 84(7):2489–2495. Model: human trial. PMID 10404825
8. Bisi G, Podio V, Valetto MR, Broglio F, Bertuccio G, Aimaretti G, Pelosi E, Del Rio G, Muccioli G, Ong H, Boghen MF, Deghenghi R, Ghigo E. Cardiac effects of hexarelin in hypopituitary adults. European Journal of Pharmacology, 1999; 381(1):31–38. Model: human trial. PMID 10528131
9. Broglio F, Benso A, Valetto MR, Gottero C, Quaranta L, Podio V, Arvat E, Bobbio M, Bisi G, Ghigo E. Growth hormone-independent cardiotropic activities of growth hormone-releasing peptides in normal subjects, in patients with growth hormone deficiency, and in patients with idiopathic or ischemic dilated cardiomyopathy. Endocrine, 2001; 14(1):105–108. Model: human trial. PMID 11322491
10. Bodart V, Febbraio M, Demers A, McNicoll N, Pohankova P, Perreault A, Sejlitz T, Escher E, Silverstein RL, Lamontagne D, Ong H. CD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart. Circulation Research, 2002; 90(8):844–849. Model: rodent. PMID 11988484
11. Frieboes RM, Antonijevic IA, Held K, Murck H, Pollmächer T, Uhr M, Steiger A. Hexarelin decreases slow-wave sleep and stimulates the secretion of GH, ACTH, cortisol and prolactin during sleep in healthy volunteers. Psychoneuroendocrinology, 2004; 29(7):851–860. Model: human trial. PMID 15177700
12. Huang J, Li Y, Zhang J, Liu Y, Lu Q. The growth hormone secretagogue hexarelin protects rat cardiomyocytes from in vivo ischemia/reperfusion injury through interleukin-1 signaling pathway. International Heart Journal, 2017; 58(2):257–263. Model: rodent. PMID 28321024
13. Sigalos JT, Pastuszak AW. The safety and efficacy of growth hormone secretagogues. Sexual Medicine Reviews, 2018; 6(1):45–53. Model: review. PMID 28400207
14. Meanti R, Licata M, Rizzi L, Bresciani E, Molteni L, Coco S, Locatelli V, Omeljaniuk RJ, Torsello A. Protective effects of hexarelin and JMV2894 in a human neuroblastoma cell line expressing the SOD1-G93A mutated protein. International Journal of Molecular Sciences, 2023; 24(2):993. Model: in vitro. PMID 36674509

Research use only

Hexarelin is supplied and described for laboratory research use only. It is not a medicine, it holds no marketing authorisation in the United Kingdom or elsewhere, and it is not authorised for human or veterinary use. Nothing in this entry is a statement that hexarelin treats, prevents or modifies any condition in humans or animals, and nothing in it constitutes medical advice, a recommendation, or guidance on administration.

The literature summarised above is reported as a record of what published studies investigated and what their authors concluded. A finding reported by a study is a fact about that study. It is not a property attributed to the compound by NovoVita, and it should not be read as one.

Hexarelin is prohibited in sport at all times under WADA Prohibited List class S2.2.4. Anyone subject to anti-doping regulation should treat this as determinative.