Two versions exist, and the difference is duration by design. Most people don't realise why there are two.
CJC-1295
CJC-1295 is a synthetic analogue of growth hormone-releasing hormone, built on the first 29 amino acids of GHRH, the segment carrying its biological activity. Four amino acid substitutions were introduced to resist enzymatic cleavage by DPP-IV. The compound exists in two forms sharing that same backbone.
The DAC in CJC-1295 with DAC stands for Drug Affinity Complex: a linker that reacts with cysteine-34 on circulating albumin to form a covalent bond. Because albumin itself has a long plasma residence, the conjugated peptide is carried with it, and the reported half-life extends from roughly 30 minutes to approximately six to eight days. The version without DAC, also called modified GRF(1-29), lacks that linker and clears rapidly. They are not interchangeable: one produces a sustained signal, the other a brief pulse.
A 2006 phase 1 randomised placebo-controlled trial by Teichman and colleagues in the Journal of Clinical Endocrinology and Metabolism reported dose-dependent elevations in growth hormone and sustained elevations in IGF-1 following a single subcutaneous dose of the DAC form. Covalent albumin conjugation as a half-life extension strategy has since appeared in approved medicines; semaglutide achieves weekly dosing by a related fatty-acid-mediated approach.