GHRP-6

Overview

GHRP-6 is a synthetic hexapeptide (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) growth hormone secretagogue and ghrelin receptor agonist. Developed by Bowers and Momany and first described in 1984, it was the first synthetic GHRP characterized and is defined by its pronounced appetite-stimulating effect — the strongest of any clinically studied GHRP. It has never been approved by the FDA or any regulatory agency and remains a research-only compound used off-label in the grey market.

Mechanism of Action

GHRP-6 binds the growth hormone secretagogue receptor 1a (GHSR-1a) on pituitary somatotrophs and hypothalamic neurons, mimicking endogenous ghrelin. Receptor activation (Gq/PLC/IP3) drives intracellular calcium release and pulsatile GH secretion while suppressing somatostatin tone. GHSR-1a activation in the arcuate nucleus strongly stimulates appetite — the hallmark feature of GHRP-6 and its defining difference from the selective GHRP ipamorelin. Compared with GHRP-2, GHRP-6 is generally less potent for raw GH output but more potent for appetite, and both produce modest transient elevations in ACTH, cortisol, and prolactin.

Research Summary

Bowers, Momany, Reynolds, and Hong first described GHRP-6 in Endocrinology (1984), making it the prototype synthetic GH secretagogue and a key tool in the later discovery of the ghrelin receptor. Ghigo et al. (1997) reviewed the GHRP class and confirmed GH, ACTH/cortisol, and prolactin co-stimulation patterns in humans. Berlanga et al. (Clinical Science, 2007; and a 2017 historical review) demonstrated cytoprotective and cardioprotective effects in myocardial infarction and ischemia-reperfusion models, attributed to antioxidant and CD36-mediated mechanisms independent of GH release. GHRP-6 has never been approved for any clinical indication.

Dosing Information

Reported Side Effects

• Intense hunger within 15–20 minutes (hallmark feature)
• Water retention and bloating
• Facial flushing
• Lethargy or drowsiness
• Transient rise in ACTH, cortisol, and prolactin
• Tingling or numbness in extremities
• Injection-site reactions
• Insulin resistance with chronic use (theoretical)

Research References

• On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone (Bowers et al.) (1984)
• Growth hormone-releasing peptides (Ghigo et al.) (1997)
• Growth-hormone-releasing peptide 6 (GHRP6) prevents oxidant cytotoxicity and reduces myocardial necrosis in a model of acute myocardial infarction (Berlanga et al.) (2007)
• Synthetic Growth Hormone-Releasing Peptides (GHRPs): A Historical Appraisal of the Evidences Supporting Their Cytoprotective Effects (Berlanga-Acosta et al.) (2017)