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GHRH analogs, ghrelin-receptor secretagogues, IGF-1 variants, and myostatin inhibitors that modulate the GH axis and skeletal-muscle growth signaling.
The growth hormone (GH) axis is controlled by two opposing hypothalamic signals: growth hormone–releasing hormone (GHRH), which stimulates pulsatile GH secretion from the anterior pituitary, and somatostatin, which inhibits it. A third input — the endogenous ghrelin receptor (GHSR-1a) — also potentiates GH release. Synthetic peptides in this category fall along those axes.
GHRH analogs include sermorelin (amino acids 1-29 of endogenous GHRH), CJC-1295 (a tetra-substituted GHRH with an optional DAC tag that extends plasma half-life by binding serum albumin), and tesamorelin (FDA-approved as Egrifta for HIV-associated lipodystrophy). Ghrelin-receptor agonists — the "growth hormone releasing peptides" or GHRPs — include ipamorelin, hexarelin, GHRP-2, and GHRP-6. Stacking a GHRH analog with a GHRP produces additive GH release in research models, which is why vendors routinely sell CJC-1295 and ipamorelin as a paired kit.
Downstream of GH sits insulin-like growth factor 1 (IGF-1), the primary mediator of GH's anabolic effects on tissue. Research analogs IGF-1 DES(1-3) and IGF-1 LR3 were engineered to evade IGF binding proteins and prolong activity. MGF (mechano growth factor) and its pegylated form PEG-MGF are splice variants of the IGF-1 gene produced locally by damaged skeletal muscle. HGH Fragment 176-191 is a lipolytic C-terminal fragment of growth hormone studied for fat-metabolism effects without the mitogenic activity of full-length GH.
The category also includes myostatin-pathway inhibitors — ACE-031 (a soluble ActRIIB decoy receptor developed by Acceleron, discontinued during clinical trials) and Follistatin-344 (a splice variant of follistatin that binds and sequesters myostatin and related TGF-β ligands).
Only sermorelin and tesamorelin hold FDA approvals, each for narrow clinical indications. All other members are research-use-only and not authorized for athletic or performance contexts.