Ipamorelin and CJC-1295 without DAC (also known as Modified GRF 1-29 or Mod GRF 1-29) represent two complementary pathways of growth hormone (GH) axis stimulation. Ipamorelin acts at the ghrelin receptor (GHSR-1a) as a growth hormone secretagogue (GHS), while CJC-1295 no DAC is a growth hormone releasing hormone (GHRH) analogue. Research into their combined use examines synergistic GH pulse amplification.
Ipamorelin (Ala-His-D-2-Nal-D-Phe-Lys-NH₂) is a synthetic pentapeptide that selectively agonises GHSR-1a — the receptor for ghrelin — to stimulate pituitary GH secretion. Its selectivity profile distinguishes it from earlier GHRPs: unlike GHRP-6, ipamorelin does not significantly stimulate cortisol or prolactin secretion at effective GH-releasing doses, and unlike GHRP-2, it shows minimal ghrelin-mediated orexigenic effects.
In vitro studies and rat anterior pituitary preparations demonstrate ipamorelin stimulates GH release in a dose-dependent manner with EC₅₀ in the nanomolar range. Fehm et al. and subsequent work established that ipamorelin-induced GH peaks are of shorter duration than exogenous GH administration, more closely mimicking physiological pulsatile secretion.
CJC-1295 without DAC (Mod GRF 1-29) is based on the first 29 amino acids of endogenous GHRH, with four amino acid substitutions that confer resistance to dipeptidyl peptidase-IV (DPP-IV) cleavage and oxidative degradation. The "no DAC" designation distinguishes it from CJC-1295 with DAC (a drug affinity complex variant with a lysine-maleimide linker for albumin binding), which has a substantially longer half-life of approximately 6–8 days.
Without the DAC modification, the half-life of Mod GRF 1-29 is approximately 30 minutes — producing a discrete GH pulse rather than sustained GH elevation. This makes it suitable for research models where pulsatile GH characteristics are important, as continuous GH elevation can downregulate GH receptors and produce different downstream IGF-1 profiles.
Pituitary GH release is regulated by two opposing hypothalamic signals: GHRH (stimulatory) and somatostatin (inhibitory). GHRPs including ipamorelin amplify GH release both by direct GHSR-1a agonism and by suppressing somatostatin tone. Combining a GHRH analogue with a GHRP therefore acts at two independent nodes of GH regulation simultaneously.
Khorram et al. (1997) and earlier work by Bowers demonstrated that combined GHRH + GHRP administration produces GH pulses approximately 2–10× greater than either agent alone in human subjects, depending on dose and timing. Ipamorelin paired with Mod GRF 1-29 is one of the most studied combinations for this synergistic effect, with both compounds timed to peak plasma concentrations simultaneously.
GH secreted in response to ipamorelin/CJC-1295 no DAC stimulates hepatic IGF-1 production. IGF-1 is the primary mediator of GH's anabolic, lipolytic, and connective tissue effects. Research in GH-deficient rodent models has demonstrated improvements in lean body mass, bone mineral density, and wound healing with GHRP/GHRH combination protocols. Human trial data is more limited but supports IGF-1 elevation with repeated dosing.
Chronic GHSR-1a stimulation leads to receptor internalisation and reduced GH pulse amplitude over time. Research protocols examining long-term GH secretagogue use typically include rest periods or alternate dosing schedules to preserve receptor sensitivity. The shorter acting Mod GRF 1-29 (vs CJC-1295 DAC) is preferred in research contexts where pulsatile pattern is important for receptor physiology studies.
These compounds are used in preclinical and in-vitro research examining GH deficiency models, muscle wasting, adipose lipolysis, and connective tissue repair. Their well-characterised pharmacology and established safety profile in acute studies make them valuable tools for GH axis investigation without the pharmacokinetic complexity of recombinant GH.
