GHRP

Growth-hormone-releasing peptides (GHRPs) are a family of synthetic peptides that stimulate pulsatile growth-hormone release through agonism of the growth-hormone secretagogue receptor (GHSR, the ghrelin receptor) rather than through the GHRH pathway. The class originated from the hexapeptide His-d-Trp-Ala-Trp-d-Phe-Lys-NH₂ characterised by Bowers in the 1970s and now includes GHRP-2, GHRP-6, hexarelin, ipamorelin, and the orally active small molecule MK-677 (ibutamoren). Pharmacologically, GHRPs combine direct somatotroph stimulation with suppression of somatostatin tone and amplification of endogenous GHRH signalling, producing a coordinated GH pulse larger than either pathway can elicit alone. The combination of a GHRH analogue (e.g. sermorelin) with a GHRP (e.g. ipamorelin) is a standard research protocol that exploits this dual-pathway synergy. Differences across the class — ipamorelin is highly selective for GH with minimal cortisol/prolactin spillover; GHRP-6 has notable appetite-stimulating effects via ghrelin mimicry — guide selection for specific research questions.