one molecule, two forms

CJC-1295 No DAC vs DAC: The Half-Life Distinction

The same tetrasubstituted hGRF(1-29) sequence forks two ways. One adds an albumin tether and lasts days; one does not and lasts minutes to hours. The single fact most worth getting right.

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The fork, drawn out

CJC-1295 no DAC and CJC-1295 DAC start from the same place: a tetrasubstituted hGRF(1-29) peptide, four substitutions blocking the proteases that clear native GHRH ^[7]. From that shared root the molecule branches once, on a single chemical feature — whether or not it carries the albumin-binding handle.

The DAC branch adds a maleimidopropionyl linker that bonds covalently to Cys34 of circulating serum albumin, producing a peptide-albumin conjugate that circulates for days ^[7]. The no-DAC branch leaves that handle off. Same sequence, same receptor target, opposite duration. This is the distinction marketing copy and forum posts most often blur, and it is the reason a 5.8-to-8.1-day figure and a minutes-to-hours figure both get attached to "CJC-1295" as if they described one thing. They do not — they describe the two ends of this fork.

Modified GRF (1-29): The No-DAC Sibling

Modified GRF (1-29) is the no-DAC form: the tetrasubstituted GHRH(1-29) sequence without the albumin-binding DAC moiety, and therefore short-acting ^[7]. It is the sibling most often conflated with CJC-1295 in community discussion, because it shares the four substitutions and the GHRH-receptor mechanism. What it does not share is duration. Lacking the albumin tether, it clears on the timescale of native GHRH(1-29) — minutes to hours — with protease resistance added by the substitutions ^[7]. Early pharmacokinetic work on native GRF(1-29)NH2 in healthy men quantified that short circulating half-life, which is exactly the limitation the DAC modification was built to overcome ^[6].

CJC-1295 DAC: Albumin Bioconjugation and Multi-Day Half-Life

CJC-1295 DAC is the long-acting form. The DAC — Drug Affinity Complex — modification functionalizes a C-terminal lysine with a maleimidopropionyl group that undergoes Michael addition with the free thiol on Cys34 of serum albumin, forming a covalent peptide-albumin conjugate and extending plasma residence toward that of albumin itself ^[7]. Jette and colleagues identified CJC-1295 as the lead among hGRF(1-29)-albumin bioconjugates: in rats it produced a 4-fold increase in GH area-under-the-curve over two hours versus unconjugated hGRF(1-29) and remained detectable in plasma beyond 72 hours ^[7]. In healthy adults, the DAC form's estimated half-life is 5.8 to 8.1 days, with IGF-1 elevation persisting up to 28 days after multiple doses ^[1]. That multi-day residence is the entire functional difference between the two forms.

CJC-1295 Half-Life: 5.8-8.1 Days (DAC) vs Minutes-to-Hours (No-DAC)

The CJC-1295 half-life splits cleanly along the fork. The DAC form's estimated half-life is 5.8 to 8.1 days in healthy adults, the figure established by Teichman and colleagues, with IGF-1 staying above baseline up to 28 days after repeated dosing ^[1]. The no-DAC Modified GRF (1-29) is short-acting, on the order of minutes to hours, reflecting native GHRH(1-29) clearance with protease resistance ^[7]. The DAC vs no-DAC half-life gap is roughly three orders of magnitude in duration — and it is why the two forms cannot be used interchangeably in any honest description of the compound.

What is CJC-1295 with DAC?

CJC-1295 with DAC carries a maleimidopropionyl linker that covalently binds circulating serum albumin, extending plasma residence to a multi-day half-life; the no-DAC form lacks this and is short-acting ^[7]. The albumin tether is the single feature separating the two.

What is CJC-1295 DAC?

"DAC" is the Drug Affinity Complex modification that conjugates the peptide to albumin; CJC-1295 DAC is the long-acting form, distinct from the short-acting no-DAC Modified GRF (1-29) ^[7]. The estimated DAC half-life of 5.8 to 8.1 days ^[1] is what "long-acting" means here in concrete terms.