Educational reference, not medical advice. This page summarizes information from published research and regulatory filings for educational purposes. It is not a recommendation to use any compound and should not replace guidance from a licensed healthcare provider. Most peptides discussed here are not approved for the uses described.
What it is
GHRP-6 is a synthetic hexapeptide (His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂) that activates the growth hormone secretagogue receptor (GHSR-1a) on pituitary somatotrophs and hypothalamic neurons. It was the first compound shown to release growth hormone through a pathway separate from GHRH, and its discovery is what eventually led to the identification of ghrelin — the natural ligand of GHSR-1a — in 1999.
GHRP-6 is the prototype of the entire ghrelin-receptor agonist class, which includes GHRP-2, hexarelin, ipamorelin, and the orally active small molecule MK-677.
History
Cyril Bowers and colleagues at Tulane University began screening enkephalin analogs for growth hormone-releasing activity in the late 1970s. The 1982 publication describing GHRP-6 reported a compound that released GH in vitro and in vivo through a mechanism distinct from GHRH. For nearly two decades, the receptor responsible was known only as "the GHRP receptor" or GHSR.
The receptor was cloned in 1996 by a Merck team, and in 1999 a group at the National Cancer Center in Tokyo identified ghrelin in the stomach as the endogenous ligand — making GHRP-6 a historical pharmacological probe that helped uncover an entire neuroendocrine system.
GHRP-6 itself was investigated for several clinical indications in the 1990s and 2000s — short stature, adult growth hormone deficiency, and wound healing — but was eventually overtaken by more selective successors (GHRP-2, ipamorelin) and the orally available MK-677. It has never been advanced to FDA approval.
Regulatory status
GHRP-6 has no approved medical use in any major jurisdiction. The FDA has not approved it; it is not on the 503A bulk substances list and compounding for patients is not permitted in the United States. The European Medicines Agency has not authorized it.
The World Anti-Doping Agency lists GHRP-6 under class S2 of the Prohibited List (peptide hormones, growth factors, related substances, and mimetics) — banned in and out of competition. GHRP-6 has been detected in multiple anti-doping cases.
Mechanism
Published mechanism papers describe GHRP-6 as a ghrelin-receptor agonist with two sites of action:
- Pituitary somatotrophs — direct activation of GHSR-1a stimulates phospholipase C signaling, raises intracellular calcium, and triggers growth hormone release.
- Hypothalamic neurons — GHRP-6 amplifies endogenous GHRH release and reduces somatostatin tone, producing a larger GH pulse than GHRH stimulation alone.
The Pandya et al. 1998 paper demonstrated this dual mechanism: blocking endogenous GHRH largely abolishes the GH response to GHRP-6, indicating that the hypothalamic component is required for maximal effect.
GHRP-6 is less receptor-selective than ipamorelin. It reliably increases appetite (consistent with its activity at ghrelin receptors), raises cortisol and ACTH, and modestly raises prolactin.
Half-life and dosing intervals
Published plasma half-life data put GHRP-6 at approximately 2.5 hours after subcutaneous injection — longer than GHRP-2 and sermorelin but shorter than DAC-modified analogs. The duration is long enough to produce a discrete GH pulse but short enough that natural pulsatility is preserved.
In published clinical studies the doses used ranged from 0.25 to 2 mcg/kg intravenously, with the higher end producing peak GH responses. In observational subcutaneous use, doses of 100 to 300 mcg per injection are commonly described, given one to three times daily. These doses are not based on a controlled efficacy trial.
Reconstitution example
GHRP-6 is sold lyophilized in 5 mg or 10 mg vials. A 5 mg vial reconstituted with 2 mL of bacteriostatic water yields 2.5 mg/mL — on a 1 mL U-100 insulin syringe, 10 units (0.1 mL) contains 250 mcg.
A 10 mg vial reconstituted with 2 mL of bacteriostatic water yields 5 mg/mL — 10 units then contains 500 mcg. Vial's calculator handles the unit-to-microgram conversion automatically.
What to know
- Historical importance, no approved use. GHRP-6 was the pharmacological tool that led to the discovery of ghrelin and the GHSR-1a receptor. It has never been approved for any therapeutic indication.
- Not FDA approved. Compounding pharmacies in the United States are not permitted to prepare GHRP-6 for patients.
- WADA banned. Use is prohibited in competitive sport.
- Pronounced hunger and cortisol effects. GHRP-6 is the least receptor-selective of the common ghrelin agonists — it reliably triggers hunger and modestly raises cortisol, ACTH, and prolactin.
- Reported side effects in observational use include strong hunger within 30 minutes of injection, water retention, transient lethargy, and injection-site reactions. Long-term safety has not been characterized in a controlled trial.
- Storage. Lyophilized vials are best stored refrigerated. Once reconstituted, refrigerate and use within 4 weeks per typical supplier stability data.
Sources
- 1.Bowers CY (1998). Growth hormone-releasing peptide (GHRP). Cellular and Molecular Life Sciences.
- 2.Pandya N et al. (1998). Growth hormone (GH)-releasing peptide-6 requires endogenous hypothalamic GH-releasing hormone for maximal GH stimulation. Journal of Clinical Endocrinology & Metabolism.
- 3.Smith RG et al. (2001). Growth hormone secretagogue receptor family members and ligands. Endocrine.
- 4.Sigalos JT, Pastuszak AW (2018). The Safety and Efficacy of Growth Hormone Secretagogues. Sexual Medicine Reviews.
- 5.World Anti-Doping Agency — Prohibited List (S2).