Encyclopedia

GHRP-6 is the original growth hormone-releasing hexapeptide, developed in 1984 as the first compound shown to stimulate GH release through a mechanism independent of GHRH. It acts as an agonist at the ghrelin receptor (GHS-R1a) and is distinguished from later GHRPs like ipamorelin by pronounced appetite stimulation and modest cortisol/prolactin elevation. It is not FDA-approved.

GHRP-6 (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) is a synthetic met-enkephalin analog discovered by Cyril Bowers at Tulane University through structure-activity screening of unnatural D-amino-acid-substituted enkephalin derivatives. Its 1984 characterization was a landmark finding, demonstrating a second, GHRH-independent pathway for pituitary GH secretion; this research program directly led to identification of the growth hormone secretagogue receptor (GHS-R1a) in 1996 and discovery of its endogenous ligand, ghrelin, in 1999. GHRP-6 has no opioid receptor activity despite its enkephalin origin. Compared to later-generation GHRPs (GHRP-2, hexarelin, ipamorelin), it produces the strongest appetite-stimulating effect of the class and a broader hormonal footprint, including modest cortisol and prolactin elevation at higher doses. It also binds the CD36 scavenger receptor, which has been explored for cardioprotective and cytoprotective properties distinct from its GH-releasing activity.

Mechanism of Action

Agonist at the growth hormone secretagogue receptor (GHS-R1a, the ghrelin receptor) on pituitary somatotrophs, stimulating GH release through a pathway distinct from and synergistic with GHRH signaling. Also binds the CD36 scavenger receptor. Unlike more selective later-generation GHRPs, it produces meaningful ghrelin-receptor-mediated appetite stimulation and modest ACTH/cortisol and prolactin release at higher doses.