What Is Hexarelin? Sequence, Salt Form and Research

Cover illustration: AI-generated editorial artwork. Conceptual only; not an exact molecular structure, actual laboratory result or evidence of clinical effects.

Hexarelin differs from the better-known GHRP-6 by a single methyl group. That is a useful starting point, because it makes hexarelin a clean illustration of how small a chemical change can be while still producing a distinct compound with its own literature — in this case a literature that has drifted largely away from growth hormone and towards the heart.

For laboratory research use only. The research materials supplied by HealthyWelness are not approved medicines, foods or cosmetics and are not for human or veterinary use. This article summarises published research and is not medical advice.

Structure

Property	Value
Sequence	His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH₂
Length	6 residues
Modification vs GHRP-6	2-methyl group on the D-Trp indole ring
Non-natural residues	D-2-methyl-Trp, D-Phe
C-terminus	Amidated
Usual salt form	Acetate

Ring methylation of a tryptophan is a standard medicinal-chemistry manoeuvre. It adds steric bulk at a position where proteolysis or unwanted conformational freedom occurs, and it modestly raises hydrophobicity. The practical analytical signature is that hexarelin elutes later than GHRP-6 under the same reverse-phase conditions and differs in mass by 14 Da — a difference small enough that a low-resolution spectrum should not be relied on to tell the two apart.

As with the rest of this peptide family, the D-amino acids are mass-silent. A batch with the wrong stereochemistry at position 2 or 5 has the correct molecular weight. Chromatography, not mass spectrometry, is the method that catches that failure, which is one reason a certificate reporting only a mass confirmation is incomplete for these compounds.

Two literatures, not one

Hexarelin’s published work splits into a pituitary strand and a cardiovascular strand, and conflating them produces confusion.

The pituitary strand places hexarelin in the secretagogue series acting at GHS-R1a. The 2000 study by Papotti and colleagues is relevant across the whole family: it documented growth hormone secretagogue binding sites in peripheral human tissues, establishing that the receptor population is not restricted to the pituitary gland.

The cardiovascular strand is where hexarelin is distinctive. The 2014 review by Mao and colleagues in the Journal of Geriatric Cardiology collects this work and is the appropriate entry point. It discusses cardiac effects reported in animal preparations and the proposal that some of them involve CD36 rather than GHS-R1a — that is, a receptor outside the secretagogue system entirely.

The 2017 study by Huang and colleagues in International Heart Journal is an example of the primary work in that strand, examining cardiomyocyte protection in a rat ischaemia–reperfusion model and implicating interleukin-1 signalling. Separately, the 2017 study by Mosa and colleagues in Endocrinology reported effects on lipid metabolic measures in a non-obese insulin-resistant mouse model, which is a metabolic rather than cardiac readout.

What the rodent kinetics tell a laboratory

The 2000 paper by Roumi and colleagues in Drug Metabolism and Disposition is the most directly useful study for experimental planning, because it characterised kinetics and disposition in rats rather than a biological effect. Short peptides of this kind are cleared quickly, and the measured behaviour in a rodent sets expectations for exposure duration in an animal model.

Two design consequences follow:

Timing of sampling matters more than it would for a long-lived agent. A readout taken on the wrong schedule can miss the exposure window altogether and read as a null result.
Comparisons with long-acting analogues are not like-for-like. Contrasting hexarelin with a modified peptide that persists far longer conflates potency with duration, which is a recurring interpretive error in this compound class.

Comparing within the family

	Hexarelin	GHRP-6	Ipamorelin
Length	6	6	5
Trp content	Two (one methylated)	Two	None
Characterised as selective	No	No	Yes, in the original report
Separate non-pituitary literature	Substantial, cardiac	Cytoprotection	Limited
Oxidation sensitivity	High	High	Lower

The last row is a handling point rather than a pharmacological one, and it is easy to overlook. A peptide with no tryptophan and no histidine is simply a more forgiving reagent. When results differ between hexarelin and ipamorelin arms of an experiment, degradation of the former is a hypothesis that should be excluded before a pharmacological explanation is adopted.

Handling

Store sealed lyophilized powder at −20 °C or below, protected from light; the methylated indole is still an oxidisable indole.
Reconstitute gently down the vial wall; do not vortex a Trp-rich peptide harder than necessary.
Use a low-metal diluent. Trace metal ions catalyse oxidation at histidine and tryptophan, a route documented in detail for model peptides.
Aliquot immediately after reconstitution and record the date. See lyophilized peptide storage.
Derive molarity from net peptide content, since the acetate counterion and residual water both contribute to vial weight. Our reconstitution calculator works from those inputs.

Our hexarelin acetate research material is supplied for laboratory research use. Certificates are available for listed products — contact us for the latest report.

Open questions

How much of the reported cardiac activity is GHS-R1a-independent, and is CD36 involvement established or proposed?
Does ring methylation measurably change oxidative stability as well as proteolytic stability?
Can the pituitary and cardiac actions be separated with a more selective analogue?

Frequently asked questions

What is hexarelin?

Hexarelin is a synthetic hexapeptide of the growth hormone releasing peptide series, His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2. It acts at the growth hormone secretagogue receptor GHS-R1a and has been studied separately for actions in cardiac tissue.

What does hexarelin acetate mean?

Acetate is the counterion supplied with the peptide. Basic peptides are isolated as salts after purification; acetate is a common form after ion exchange. The acetate mass is part of the vial weight but not part of the peptide.

How does hexarelin differ from GHRP-6?

The difference is one modification: the D-tryptophan at position 2 carries a methyl group on the indole ring. The rest of the sequence is the same. That single change alters metabolic stability and receptor interaction.

Why is hexarelin studied in cardiac tissue?

Published work describes binding sites and effects in cardiac preparations that are discussed as distinct from the pituitary growth hormone axis, including a proposed interaction with CD36. This is the basis of the separate cardiovascular literature.

Is hexarelin stable in solution?

Not indefinitely. It contains two tryptophan residues and a histidine, all oxidation-prone, and rodent kinetic work reports rapid clearance. In the laboratory it is handled as a light-sensitive peptide and aliquoted after reconstitution.

References

Mao Y, et al. The cardiovascular action of hexarelin. J Geriatr Cardiol. 2014. PMID: 25278975 https://pubmed.ncbi.nlm.nih.gov/25278975/
Roumi M, et al. Kinetics and disposition of hexarelin, a peptidic growth hormone secretagogue, in rats. Drug Metab Dispos. 2000. PMID: 10611139 https://pubmed.ncbi.nlm.nih.gov/10611139/
Papotti M, et al. Growth hormone secretagogue binding sites in peripheral human tissues. J Clin Endocrinol Metab. 2000. PMID: 11061542 https://pubmed.ncbi.nlm.nih.gov/11061542/
Mosa R, et al. Hexarelin, a Growth Hormone Secretagogue, Improves Lipid Metabolic Aberrations in Nonobese Insulin-Resistant Male MKR Mice. Endocrinology. 2017. PMID: 28977588 https://pubmed.ncbi.nlm.nih.gov/28977588/
Huang J, et al. The Growth Hormone Secretagogue Hexarelin Protects Rat Cardiomyocytes From in vivo Ischemia/Reperfusion Injury Through Interleukin-1 Signaling Pathway. Int Heart J. 2017. PMID: 28321024 https://pubmed.ncbi.nlm.nih.gov/28321024/