Summary

GHRP-6 (Growth Hormone Releasing Peptide-6) is a synthetic hexapeptide that acts on the ghrelin receptor (GHS-R1a) to stimulate growth hormone release from the pituitary gland. As one of the earliest discovered GHRPs, it helped establish the field of growth hormone secretagogues. It is studied for GH release, appetite stimulation, and synergistic effects when combined with GHRH analogues. GHRP-6 also transiently raises cortisol and prolactin, distinguishing it from more selective secretagogues like ipamorelin.

Mechanism

GHRP-6 is a ghrelin receptor (GHS-R1a) agonist. Binding to the ghrelin receptor on somatotroph cells in the anterior pituitary triggers GH release via a Gq/11-mediated signalling cascade. This pathway is complementary to (and synergistic with) the GHRH receptor pathway. GHRP-6 also activates ghrelin receptors in other tissues, which mediates its appetite-stimulating effects and may contribute to off-target effects on cortisol and prolactin.

Evidence base

GHRP-6 has a moderate body of human pharmacological data demonstrating GH-releasing activity and synergy with GHRH (Bowers et al., 1984; 1993). It also transiently raises cortisol and prolactin, distinguishing it from more selective secretagogues (Raun et al., 1998). Appetite stimulation via ghrelin receptor activation is documented in humans and animals (Kalra et al., 2003). Long-term human safety data is lacking.

Protocols

In published human studies, GHRP-6 has been administered subcutaneously at approximately 1–5 µg/kg and intravenously at 0.1–1.0 µg/kg (Bowers et al., 1984). It is commonly discussed alongside a GHRH analogue for synergistic GH release, with administration 2–3 times daily and cycles of 4–8 weeks referenced. These are research protocols, not medical dosing instructions.

GHRP-6 is not a UK-licensed medicine and is not a controlled substance. It falls into a grey area — legal to purchase and possess for research purposes, but not approved by the MHRA for human therapeutic use. Should be sold for research purposes only.

Vendor notes

No UK vendors have been independently verified for GHRP-6 at this time. Researchers should follow the guidance in our Vendor Vetting Guide when evaluating suppliers.

References

  1. Bowers CY, Momany FA, Reynolds GA, Hong A. On the in vitro and in vivo activity-independent, in vivo potency, of the synthetic hexapeptide, GHRP-6. Endocrinology. 1984;114(5):1537-1545.
  2. Bowers CY, Reynolds GA, Durham D, et al. Growth hormone (GH)-releasing peptide stimulates GH release in normal men and acts synergistically with GH-releasing hormone. Journal of Clinical Endocrinology & Metabolism. 1993;77(6):1485-1492.
  3. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology. 1998;139(5):552-561.
  4. Rahim A, Toogood AA, Shalet SM. The effect of varying subcutaneous doses of hexarelin on growth hormone, prolactin and cortisol release in normal human volunteers. Journal of Endocrinology. 1995;147(1):147-152.
  5. Kalra SP, Ueno N, Kalra PS. Stimulation of appetite by ghrelin is regulated by leptin restraint: peripheral and central sites of action. Journal of Nutrition. 2003;133(2):449-453.