Research guides

GHRP-6: what the research says

The first growth hormone releasing peptide, and the one whose lack of selectivity is why every later secretagogue exists. It also raises cortisol and appetite.

Available in the catalogue

Supplied as research material. Sizes and pricing are on the product page. Availability is not a statement about what a compound does.

GHRP-6 is the compound the rest of this class was designed to improve on. Reading it as simply an older, weaker ipamorelin misses the point: what it does beyond releasing growth hormone is the finding, not a footnote to it.

What the molecule is

A synthetic hexapeptide, the first of the growth hormone releasing peptides, characterised by Cyril Bowers and colleagues in the 1980s. Its historical significance is larger than its own pharmacology: the search for the natural ligand of the receptor these peptides were hitting is what eventually led to the discovery of ghrelin, more than a decade later.

Two receptors, not one

The published work describes activity at GHS-R1a, the ghrelin receptor, which is the route to pituitary growth hormone release. A separate strand of the literature describes binding at CD36, a scavenger receptor found in cardiac and other tissue, and it is that second receptor which the cytoprotection literature on this family is built around. The two are distinct targets and a summary that mentions only the first is describing half the molecule.

Selectivity, and why it matters here

The defining property of GHRP-6 in the published record is that it is not selective. Compounds of this class stimulate appetite, and raise cortisol, ACTH and prolactin alongside growth hormone. That is the finding ipamorelin was subsequently built to avoid, and it is why the class-level human work on secretagogue selectivity — conducted with the closely related GHRP-2 and hexarelin — is the most useful safety-adjacent evidence available for reading this compound.

For a research tool the consequence is methodological rather than clinical: any effect observed after administering a non-selective secretagogue has more than one plausible endocrine explanation, so the compound is a blunt instrument for isolating growth hormone effects specifically.

What studies reported

Each entry states what a study examined and the model it used. Nothing below describes an outcome for a person.

Everything below is drawn from published research, and each entry names the model the study used. Approval status varies by compound and by country, and nothing described here is supplied as a medicine or for use in a person.

  1. Hayashi et al. (1991)Endocrinologia Japonica · 38(1):15–21

    Reported increases in plasma growth hormone and insulin-like growth factor 1 in normal men following administration of the hexapeptide.

    human, healthy men Source

  2. Berlanga-Acosta et al. (2017)Clinical Medicine Insights: Cardiology

    A historical appraisal of the GHRP family, reporting that these peptides act at two receptors — GHS-R1a and CD36 — and reviewing the cytoprotective effects described across cardiac, neuronal and hepatic tissue.

    review of preclinical and clinical work Source

  3. Bowers (2012)Methods in Enzymology · 514:3–32

    An account by the peptide's originator of how work on the growth hormone releasing peptides led to the identification of ghrelin and its receptor.

    historical review Source

Adverse and null findings reported

Harms, tolerability observations, and trials that did not meet their endpoint. A negative result is a finding and is listed here rather than omitted.

  1. Arvat et al. (1997)Peptides · 18(6):885–91

    Compared two secretagogues of this class against GHRH and other releasing hormones in man, reporting that they raised prolactin, ACTH and cortisol alongside growth hormone. The compounds studied were GHRP-2 and hexarelin rather than GHRP-6 itself, so this is class-level evidence for the non-selectivity the later compounds were designed to remove.

    human, comparative endocrine study Source

  2. Ghigo et al. (1997)European Journal of Endocrinology · 136(5):445–60

    A review of the growth hormone releasing peptides covering their endocrine activity beyond growth hormone release, and the questions this raised about their usefulness as selective tools.

    review of human and animal work Source

What the research does not establish

An absence cannot be cited, so these are stated plainly. They are the part of the picture that silence would otherwise hide.

  • No randomised controlled trial of GHRP-6 for any therapeutic indication has been published, and it holds no marketing authorisation in any jurisdiction.
  • Most of the human evidence is short single-occasion endocrine work measuring hormone release, not outcome studies. What sustained stimulation of this receptor does over months is not addressed by any published trial of this compound.
  • The cytoprotective findings attributed to the family run through CD36 rather than the growth hormone pathway, and the bulk of that evidence is preclinical. Whether it holds in humans has not been established.
  • Appetite stimulation is a consistently reported property of this class, but it has not been characterised in a controlled human study of GHRP-6 specifically.
  • The most informative selectivity data available were generated with GHRP-2 and hexarelin. Reading them across to GHRP-6 is a reasonable inference about a shared mechanism, not a measurement of this molecule.

Common questions

What is the difference between GHRP-6 and ipamorelin?
Selectivity. Both bind the ghrelin receptor and prompt pituitary growth hormone release, but published work on this class reports that the earlier peptides also raise cortisol, ACTH and prolactin and stimulate appetite. Ipamorelin was designed specifically to release growth hormone without those accompanying effects.
Has GHRP-6 been studied in humans?
Yes, in endocrine studies measuring hormone release — a 1991 study reported rises in growth hormone and IGF-1 in healthy men. There is no published randomised controlled trial of it for any therapeutic indication.
Why does GHRP-6 appear in cardiac research?
Because it binds CD36 as well as the ghrelin receptor, and CD36 is present in cardiac tissue. That second receptor, not the growth hormone pathway, is what the cytoprotection literature on this family is built around.
What is GHRP-6's connection to ghrelin?
It came first. These peptides were found to act at a receptor whose natural ligand was unknown, and the search for that ligand led to the identification of ghrelin over a decade later. The receptor is still often called the growth hormone secretagogue receptor for that reason.
Is GHRP-6 an approved medicine?
No, in any jurisdiction. It is supplied here as a laboratory reagent for in-vitro research, with a certificate of analysis, and not for human or veterinary use.

Compounds covered

The reference page for each compound this article discusses.

Related articles

  • Hexarelin (examorelin): what the research says

    One of the most potent secretagogues tested in humans, with a second cardiac literature running through CD36 rather than the growth hormone axis.

  • Ipamorelin: what the research says

    A selective growth hormone secretagogue with a completed, published human trial. It missed its primary endpoint, and that is the most useful result it has.

  • How to store research peptides

    Lyophilised peptides at -20°C, reconstituted at 2–8°C, ambient in transit. Why the dry cake tolerates shipping, and what actually degrades a vial.

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