Quick answer: Hexarelin and GHRP-6 are hexapeptides that act at the ghrelin receptor. They differ by one methyl group on residue 2, which makes hexarelin about 887 Da and GHRP-6 about 873 Da. A purity percentage cannot separate them; a measured mass on the certificate can.
Two close relatives that are easy to confuse
Hexarelin and GHRP-6 are both synthetic hexapeptides from the growth hormone-releasing peptide family. They share five of their six residues, they act at the same receptor, and they are often mentioned in the same forum thread. They are still two separate molecules with different masses, and a protocol or a notebook that names one should not be filled with the other.
This guide compares them on origin, structure, receptor background, what the published literature describes and what a certificate should show. It is background for laboratory research use only. Nothing here describes an effect or a use in people or animals. Single-compound background is in the hexarelin research overview and the nickname explainer what is hexarelin.
Origin: a 1980s hexapeptide and its modified successor
GHRP-6 came first. Cyril Bowers and colleagues described it in 1984 as a synthetic hexapeptide that released growth hormone from pituitary cells in culture and in animal models. It was built from unusual building blocks, including two D-amino acids, which was an early sign that the family was designed rather than copied from a natural hormone.
Hexarelin was developed later as a modified analog of the same template. Its design goal was a sequence that kept the receptor activity of GHRP-6 while changing one residue. Both peptides were studied long before the natural ligand for their receptor was known. That ligand, ghrelin, was identified in 1999, and it explained why a family of synthetic compounds had been releasing growth hormone through a receptor nobody had matched to a hormone.
For a wider view of how this family sits next to other secretagogues, the hexarelin vs. ipamorelin comparison covers the pentapeptide side of the family.
Side-by-side comparison
| Feature | Hexarelin | GHRP-6 |
|---|---|---|
| Family | Growth hormone-releasing peptide (hexapeptide) | Growth hormone-releasing peptide (hexapeptide) |
| Sequence | His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH2 | His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 |
| Key difference | Methyl group on residue 2 | No methyl group |
| Approximate mass | About 887 Da | About 873 Da |
| Main receptor | Ghrelin receptor (GHS-R1a) | Ghrelin receptor (GHS-R1a) |
| Other binding reported | CD36 (cardiac tissue models) | Not a feature of its literature |
| Key identity check | Measured mass near 887 Da | Measured mass near 873 Da |
| Listed by V8 | Yes, research use only | No |
Structure: one methyl group apart
GHRP-6 has the sequence His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, with an amidated C-terminus. Its molecular weight is about 873 Da. Hexarelin has the same order of residues except that the second residue is D-2-methyltryptophan instead of D-tryptophan. That single added methyl group raises the mass to about 887 Da, a difference of 14 Da.
The gap is small but it is measurable. A mass spectrometer reading about 873 Da points to GHRP-6, and one reading about 887 Da points to hexarelin. A purity percentage from HPLC cannot separate them by itself, because both are hexapeptides of similar polarity and can each show a single clean peak. This is the core reason the identity line on a certificate matters for this pair.
Both peptides are lyophilized powders. Neither has a metal, a lipid chain or a linker, so their chemistry is straightforward compared with larger analogs.
Receptor background
Both compounds act at the growth hormone secretagogue receptor type 1a, the receptor later shown to bind ghrelin. Howard and colleagues cloned the receptor in 1996, which turned a pharmacology puzzle into a defined target. The two peptides are therefore best described as ghrelin-receptor agonists in assay language.
Hexarelin has one extra thread in its literature. Work by Bodart and colleagues reported that hexarelin also binds CD36, a scavenger receptor found on several cell types, and proposed a role for that interaction in cardiac tissue models. That finding is specific to the hexarelin literature and is a reason the two peptides are not regarded as interchangeable in cell-based designs. A reader should still check each paper to see which compound was actually used.
What the published work reports
Most of the older work on both compounds is receptor pharmacology in cell lines and animal models, with additional reports on secretion patterns over repeated exposure. Several papers on hexarelin describe a fading response when the peptide is applied repeatedly in experimental systems, which is one reason repeated-exposure design is a recurring topic in this part of the literature. This guide does not summarize clinical findings, because those fall outside a research-use catalog.
The practical reading for a bench scientist is that the two peptides share a receptor and a template, differ by one methyl group, and have separate bodies of evidence. A methods section should name the exact peptide, the lot and the supplier, so that a later reader can tell which one produced the result.
What a certificate should show
For a pair this close in mass, the identity check carries most of the weight. Look for a measured mass next to the expected value, the exact compound name, and a lot identifier and test date that match the vial. For background on reading these documents, see understanding HPLC purity and how to read a COA.
A chromatogram is worth reading as well as the percentage. Solid-phase synthesis of a hexapeptide with D-amino acids can leave small populations of deletion or racemized sequences, and these may sit close to the main peak. For cell work, look for an endotoxin result and a sterility statement.
V8 Peptides publishes certificates for only some products. Where one exists, it reports HPLC purity and identity, endotoxin and PCR sterility. This article describes general buyer practice and is not a statement about any particular lot. V8 lists hexarelin at hexarelin for research use only; GHRP-6 is not part of the V8 catalog. Compound pages for hexarelin are hexarelin purity testing and where to buy hexarelin.
Handling and record keeping
Keep lyophilized peptide cold, dry and away from light until use, and write the opening date on the vial. Plan aliquots before opening so a vial is not handled repeatedly. This guide gives no volumes or concentrations, because those belong in a laboratory's own validated procedure.
In the notebook, record the exact name, lot, supplier, certificate date, storage conditions and the opening date. When two related peptides are run in one study, label them as separate reagents with separate controls from the first day.
Frequently asked questions
Are hexarelin and GHRP-6 the same peptide?
No. They share five of six residues. Hexarelin carries a methyl group on the second residue, which makes it about 14 Da heavier.
Which receptor do they act on?
Both act at the growth hormone secretagogue receptor type 1a, the receptor that also binds ghrelin.
Can HPLC purity tell them apart?
Not reliably. Both are hexapeptides of similar polarity. A measured mass next to the expected mass is the identity check.
What is the mass difference?
About 887 Da for hexarelin against about 873 Da for GHRP-6, a gap of roughly 14 Da.
Why does CD36 come up for hexarelin?
Published work reported that hexarelin binds CD36 as well as the ghrelin receptor, and that finding belongs to the hexarelin literature specifically.
Which one came first?
GHRP-6 was described in 1984. Hexarelin was developed afterward as a modified analog of the same template.
Does V8 sell GHRP-6?
No. V8 lists hexarelin, for laboratory research use only.
Why do D-amino acids matter on a certificate?
D-residues can racemize or be incorporated incorrectly during synthesis, so a chromatogram is worth reading alongside the purity figure.
Does this article describe a use in people?
No. It summarizes structure, published background and analytical practice. No product is sold for human or animal consumption.
What should I record for each vial?
The exact compound name, lot identifier, certificate date, supplier, storage conditions and the date the vial was opened.
References
- Bowers CY, Momany FA, Reynolds GA, Hong A. On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Endocrinology. 1984;114(5):1537-1545.
- Howard AD, Feighner SD, Cully DF, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273(5277):974-977.
- Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402(6762):656-660.
- 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.
- Smith RG, Van der Ploeg LH, Howard AD, et al. Peptidomimetic regulation of growth hormone secretion. Endocr Rev. 1997;18(5):621-645.