Mod GRF 1-29

Mod GRF 1-29 (Modified GRF 1-29, also known as CJC-1295 without DAC or simply "CJC without DAC") is a synthetic analogue of growth hormone-releasing hormone (GHRH), the hypothalamic peptide that triggers GH secretion from the anterior pituitary. It represents the first 29 amino acids of native GHRH - the biologically active fragment - modified at four positions to resist enzymatic degradation.

Native GHRH 1-29 (Sermorelin) has a half-life of only 2-10 minutes in serum due to rapid cleavage by dipeptidyl peptidase IV (DPP-IV) and other proteases. Mod GRF 1-29 was created by substituting amino acids at positions 2, 8, 15, and 27 with more stable alternatives. These substitutions make the peptide resistant to DPP-IV cleavage at the N-terminus (position 2 substitution) and reduce susceptibility to other proteases - extending the half-life to approximately 30 minutes while preserving high GHRH receptor affinity and biological activity.

The defining characteristic of Mod GRF 1-29 vs. CJC-1295 with DAC is the absence of the Drug Affinity Complex (DAC) - a lysine derivative that allows the peptide to bind covalently to albumin in the bloodstream. With DAC, the resulting half-life extends to 8-10 days and GH elevation becomes continuous. Without DAC (Mod GRF 1-29), the half-life is approximately 30 minutes, and the peptide produces discrete, physiological GH pulses.

Researchers working on GH axis physiology generally prefer Mod GRF 1-29 over CJC-1295 with DAC precisely because it preserves natural pulsatility. GH is normally secreted in discrete pulses 4-8 times per day, with the largest pulse occurring during deep sleep. This pulsatile pattern is important for maintaining sensitivity of GH receptors and avoiding desensitisation. CJC-1295 with DAC's continuous stimulation disrupts this pattern.

Mod GRF 1-29 is almost never used alone in research. When combined with a GHRP peptide (Ipamorelin, GHRP-2, GHRP-6, or Hexarelin), the result is a dramatic synergistic amplification of GH release that far exceeds either peptide alone. This is because the two classes target different regulatory mechanisms: Mod GRF 1-29 stimulates GH release via GHRH receptors, while GHRPs both directly stimulate GH secretion via GHS receptors AND suppress somatostatin (the GH inhibitory hormone). Together, they release the brake and press the accelerator simultaneously.