Growth Hormone Secretagogues (GHRP & GHRH)

Growth hormone secretagogues (GHS) are a class of peptides that stimulate the pituitary gland to release endogenous growth hormone (GH). The class is divided into two mechanistic subgroups: growth hormone-releasing hormone analogs (GHRH analogs), which act on GHRH receptors on somatotroph cells, and growth hormone-releasing peptides (GHRPs), which act on ghrelin receptors (GHSR-1a) to amplify GH pulse amplitude. Both subgroups work synergistically when combined, producing a supra-additive GH release.

GHRH analogs such as CJC-1295 and Sermorelin bind to the pituitary GHRH receptor, activating adenylyl cyclase, increasing intracellular cAMP, and triggering calcium-mediated GH vesicle exocytosis. GHRPs including GHRP-2, GHRP-6, Hexarelin, and Ipamorelin bind to GHSR-1a receptors on both pituitary somatotrophs and hypothalamic neurons, suppressing somatostatin (the physiological GH brake) while simultaneously amplifying GH release. When a GHRH analog and GHRP are co-administered, their complementary mechanisms produce synergistic GH secretion 2–10 times greater than either peptide alone.

The GHRH-analog Sermorelin was FDA-approved for pediatric GH deficiency (withdrawn from the US market for commercial, not safety, reasons). Tesamorelin, a GHRH analog, is FDA-approved as Egrifta for HIV-associated lipodystrophy. The GHRPs (GHRP-2, GHRP-6, Hexarelin, Ipamorelin) remain investigational compounds in the United States and are not FDA-approved for human use outside of clinical trials. Research has focused on body composition, bone density, sleep quality, and cardiac function.

All GH secretagogue research in humans must account for the pulsatile nature of GH release, the role of endogenous somatostatin tone, and the potential for GH receptor desensitization with chronic administration. Ipamorelin is widely studied for its selectivity (minimal cortisol or prolactin release vs. GHRP-6 and GHRP-2). Hexarelin shows additional cardiac receptor activity distinct from GH release. IGF-1 monitoring is standard in GHS research protocols.