GHRP-6 vs GHRP-2 vs Hexarelin vs Ipamorelin: Ghrelin-Receptor Peptides Compared

For laboratory research use only. This article compares research peptides as they are described in the published preclinical literature. It is educational only and contains no dosing, human-use, veterinary, or clinical guidance.

GHRP-6, GHRP-2, hexarelin and ipamorelin all act at the same receptor, the growth-hormone secretagogue receptor GHS-R1a, which is also the receptor for the hormone ghrelin. What separates them is selectivity. GHRP-6, GHRP-2 and hexarelin are hexapeptides that, alongside growth hormone, are reported to raise other hormones such as ACTH and cortisol, and GHRP-6 carries a strong appetite-related signal. Ipamorelin is a pentapeptide described as selective because it produces little of that spillover. Hexarelin adds a second distinguishing feature: binding to the CD36 receptor, which puts it in cardiac research as well.

One receptor, four ligands

GHS-R1a is a G-protein-coupled receptor, and ghrelin is its natural ligand. The growth-hormone-releasing peptides (GHRPs) were developed as synthetic agonists at this receptor, before ghrelin itself was discovered. That shared target is why the four are compared as a family; the differences lie in sequence, and in which other pathways each one also touches. The growth-hormone axis has a second, separate input, the GHRH receptor, which is where sermorelin, CJC-1295 and tesamorelin act; that family is compared in sermorelin vs CJC-1295 vs tesamorelin vs ipamorelin.

Sequences side by side

Peptide	Length	Sequence
GHRP-6	6 residues	His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂
GHRP-2	6 residues	D-Ala-D-2Nal-Ala-Trp-D-Phe-Lys-NH₂
Hexarelin	6 residues	His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH₂
Ipamorelin	5 residues	Aib-His-D-2Nal-D-Phe-Lys-NH₂

Hexarelin is GHRP-6 with one change: a methyl group on the tryptophan at position 2. GHRP-2 replaces GHRP-6's first two residues with D-alanine and D-2-naphthylalanine (D-2Nal). Ipamorelin keeps the D-2Nal and the C-terminal D-Phe-Lys but is one residue shorter and begins with aminoisobutyric acid (Aib).

GHRP-6

GHRP-6 is the earliest of the group and the reference point for the rest. Its most cited distinguishing feature is an appetite-related signal: because it mimics ghrelin at the ghrelin receptor, and ghrelin is studied for its role in hunger signalling, GHRP-6 produces a marked appetite-related response in animal models. That signal is reported less consistently for GHRP-2 and is largely absent from the ipamorelin literature.

GHRP-2

GHRP-2 is described in the literature as one of the more potent members of the family at the receptor. Like GHRP-6, it is reported to raise ACTH, cortisol and prolactin alongside growth hormone, which matters for any design that measures stress-axis or lactotroph endpoints. Our GHRP-2 research overview covers its profile in depth.

Hexarelin

Hexarelin shares the family's core mechanism, with two findings that set it apart:

CD36 binding. Hexarelin also binds CD36, a scavenger receptor found on heart and other tissue, which is why it appears in cardiac-tissue research in a way the other GHRPs do not. A 2014 review in the Journal of Geriatric Cardiology summarises this cardiovascular literature.
Desensitisation. Repeated-administration animal models report a progressively smaller growth-hormone response with hexarelin (tachyphylaxis), generally attributed to receptor downregulation, and more prominently than with GHRP-2.

More detail is in our hexarelin research overview.

Ipamorelin

Ipamorelin was introduced in a 1998 study in the European Journal of Endocrinology as the first selective growth-hormone secretagogue. In that work, run in animal models, it released growth hormone with potency comparable to GHRP-6 but, unlike GHRP-6 and GHRP-2, without significant increases in ACTH or cortisol. That selectivity is what makes it useful as a research tool: a cleaner input produces cleaner data, because fewer confounding pathways are stimulated at once. Ipamorelin is the one member of this family stocked on this site, as part of the CJC-1295 no-DAC + Ipamorelin research blend.

Side-by-side summary

	GHRP-6	GHRP-2	Hexarelin	Ipamorelin
Receptor	GHS-R1a	GHS-R1a	GHS-R1a, plus CD36	GHS-R1a
Length	Hexapeptide	Hexapeptide	Hexapeptide	Pentapeptide
ACTH / cortisol rise reported	Yes	Yes	Yes	Little or none
Distinguishing finding	Appetite-related signal	Potency at the receptor	Cardiac research; desensitisation	Selectivity

Choosing among them for a research design

The choice follows the question. A design isolating GHS-R1a's growth-hormone effect with as few confounding pathways as possible points to ipamorelin. A design studying ghrelin-like appetite signalling points to GHRP-6. Cardiac-tissue work involving CD36 points to hexarelin. Repeated-exposure designs need to account for hexarelin's reported desensitisation. Whatever the choice, record concentration and batch for each vial; the ratio chart covers the arithmetic.

Frequently Asked Questions

What receptor do GHRP-6 and GHRP-2 act on?

Both are agonists at the growth-hormone secretagogue receptor, GHS-R1a, the same receptor that binds the hormone ghrelin. Hexarelin and ipamorelin act there too.

What is the main difference between GHRP-6 and GHRP-2?

Their sequences differ in the first two residues, and GHRP-6 carries a strong appetite-related signal in animal models that is reported less consistently for GHRP-2. Both are reported to raise ACTH and cortisol alongside growth hormone.

Why is ipamorelin considered more selective than the GHRPs?

In the study that introduced it, ipamorelin released growth hormone without the significant rises in ACTH and cortisol seen with GHRP-6 and GHRP-2, so it stimulates fewer pathways beyond its target.