Mod-GRF 1-29 (also designated CJC-1293 without DAC, or tetrasubstituted GHRH[1-29]) is a synthetic analogue of the first 29 amino acids of growth hormone-releasing hormone, modified at four positions including substitution of norleucine at position 27 to improve proteolytic stability and extend the effective half-life of native GHRH 1-29, thereby producing more sustained pituitary GH stimulation per dose. Like endogenous GHRH, it acts through GHRH receptors on pituitary somatotrophs to stimulate cAMP-mediated GH synthesis and secretion, and is administered to mimic the hypothalamic pulse signal that drives GH release and downstream IGF-1 axis activity. Modified GHRH 1-29 analogues sharing the core amino acid substitutions of Mod-GRF 1-29, specifically [Nle27]GHRH(1-29)-NH2, have been administered to humans in controlled studies that documented sustained GH and IGF-1 axis effects with endocrine, metabolic, and immune endpoints characterized in age-advanced subjects. Mod-GRF 1-29 has not received FDA approval; the related compound sermorelin (unmodified GHRH 1-29) was previously FDA-approved for pediatric GH deficiency but was withdrawn by its manufacturer, and Mod-GRF 1-29 is an investigational compound not approved for any clinical indication. Naming note — Mod GRF 1-29 vs CJC-1295: the research compound marketplace uses several overlapping names for this compound. "Mod GRF 1-29" and "CJC-1295 without DAC" refer to the same tetrasubstituted GHRH(1-29) peptide. "CJC-1295 with DAC" (or simply "CJC-1295" in most clinical protocol contexts) is a different compound — it includes a Drug Affinity Complex (DAC) linker that enables albumin binding and produces a dramatically extended half-life (~8 days vs ~30 minutes for Mod GRF 1-29). CJC-1295 with DAC is used as an infrequent injection (weekly or biweekly) while Mod GRF 1-29 / CJC-1295 without DAC is used at each injection session, typically immediately before or alongside a GHRP such as ipamorelin to maximally leverage the GH pulse window. Research administration context: Mod GRF 1-29 is studied via subcutaneous injection in research contexts, typically in combination with a GHRP such as ipamorelin to leverage complementary GH-stimulating pathways. No validated human dosing protocol has been established for Mod GRF 1-29; doses used in combination research derive from community practice and preclinical models rather than published human dose-finding trials. Provider availability for Mod GRF 1-29 and CJC-1295 compounds is listed in the PeptideBase directory.