Sermorelin (sermorelin acetate, GHRH 1-29 NH₂) is a synthetic 29-amino-acid peptide corresponding to the biologically active N-terminal fragment of endogenous Growth Hormone Releasing Hormone (GHRH). It was FDA-approved in 1997 as Geref® for GH deficiency diagnosis and treatment in children, and has one of the longest clinical records of any synthetic GHRH analogue.
Endogenous GHRH is a 44-amino acid peptide produced by neurons in the hypothalamic arcuate nucleus. The first 29 residues (GHRH 1-29) contain the full receptor-binding domain and biologically active region; residues 30-44 are not required for receptor activation. Sermorelin is therefore the minimal bioactive fragment of GHRH and binds the GHRH receptor (GHRHR) with essentially the same affinity as the full-length peptide.
The short half-life of sermorelin (approximately 10-20 minutes) reflects rapid degradation by DPP-IV and other peptidases — a limitation that drove development of stabilised analogues including CJC-1295 and tesamorelin. Despite this short half-life, pulsatile subcutaneous injection protocols can effectively stimulate physiological GH pulses.
Sermorelin received FDA approval via Serono Laboratories as Geref® for two indications: (1) as a diagnostic agent for GH deficiency assessment (the sermorelin stimulation test as an alternative to insulin tolerance testing), and (2) for treatment of idiopathic GH deficiency in prepubertal children. Manufacturing of Geref® was discontinued in 2008 for commercial reasons, not safety concerns, but the compound remains active in clinical research and compounding.
Walker et al. and other groups conducted studies in adult GH deficiency and age-related GH decline, demonstrating that nightly sermorelin administration increases GH pulse amplitude and IGF-1 levels with a profile considered more physiological than exogenous GH injection, as it preserves pulsatility and relies on intact pituitary function.
A key research interest in GHRH analogues including sermorelin is their mechanism of action via stimulation of endogenous pituitary GH release rather than exogenous GH replacement. This has several research-relevant properties:
In adult GH deficiency research, sermorelin administration over 3-6 months has demonstrated increases in IGF-1, lean body mass, bone mineral density, and improvements in lipid profiles versus placebo. These effects are consistent with GH's known anabolic and lipolytic actions. The body composition effects are generally smaller than those seen with supraphysiological exogenous GH doses, consistent with sermorelin's physiological mechanism.
As with CJC-1295, sermorelin is frequently studied in combination with GHRPs (ipamorelin, GHRP-2, GHRP-6) to exploit synergistic GH release via dual hypothalamic-pituitary pathway activation. The shorter half-life of sermorelin versus CJC-1295 analogues means timing of concurrent GHRP administration is more important for maximising synergy.
