Pharmacokinetics · the central distinction
CJC-1295 DAC vs No-DAC: The Pharmacokinetic Difference
One form lingers in the blood for days; the other clears in minutes to hours. The two are routinely sold as the same thing. Here is what actually separates them.
The one difference that changes everything
CJC-1295 DAC vs no-DAC comes down to a single structural feature: whether the peptide carries the albumin-binding handle. The DAC variant does; the no-DAC form does not. Everything else — the four protease-resistant substitutions, the hGRF(1-29) backbone, the GHRH-receptor target — is shared. That one difference moves the half-life from minutes-to-hours to days [1].
The DAC variant raised growth hormone and IGF-1 for days after a single dose in healthy adults, with an estimated 5.8-to-8.1-day half-life [1]. The no-DAC form, lacking the albumin conjugation, clears at a rate closer to native GHRH(1-29) with the substitutions slowing enzymatic breakdown but nothing extending plasma residence. Calling both "CJC-1295" without specifying the variant collapses two pharmacokinetically opposite molecules into one word, which is the single most common error in how this compound is discussed.
What is CJC-1295 with DAC?
The DAC variant — "Drug Affinity Complex" — carries a maleimidopropionyl handle on a C-terminal lysine that covalently bonds to the free thiol on Cys34 of circulating serum albumin. The result is a peptide-albumin conjugate whose plasma half-life extends toward that of albumin itself, giving the estimated 5.8-to-8.1-day half-life measured in healthy adults [1].
The bioconjugation was demonstrated in rats before the human work. A maleimidopropionyl-lysine series was screened, and CJC-1295 emerged as the lead, showing a 4-fold increase in growth-hormone area-under-the-curve over two hours versus unconjugated hGRF(1-29), with peptide detectable in plasma beyond 72 hours [2]. The albumin tether, not the substitutions alone, is what makes the DAC form long-acting.
Modified GRF (1-29): The No-DAC Short-Acting Form
Modified GRF (1-29) is the no-DAC form: the same four-substituted hGRF(1-29) sequence without the albumin-binding moiety. It keeps the protease resistance — the D-Ala2 substitution blocks dipeptidylpeptidase-IV cleavage — but lacks the mechanism that extends plasma residence, so it is short-acting, in the minutes-to-hours range that reflects native GHRH(1-29) clearance [1].
The naming is where the confusion lives. "Modified GRF 1-29," "Mod GRF 1-29," and "CJC-1295 no-DAC" all refer to the short-acting form; "CJC-1295 DAC," "CJC-1295 with DAC," and "DAC:GRF" all refer to the long-acting conjugate. A product or protocol that says only "CJC-1295" has not specified which pharmacokinetic profile it means, and the two are not interchangeable.
For a reader doing due diligence, the practical consequence is that any duration, frequency, or kinetic claim is meaningless until the variant is named. The CJC-1295 half-life page rebuilds the full kinetic timeline for each form.
Same target, same backbone, opposite kinetics
It helps to be precise about what the two forms share and what they do not. Both bind the same growth-hormone-releasing hormone receptor on pituitary somatotrophs. Both carry the same four substitutions on the hGRF(1-29) backbone — D-Ala at position 2, Gln at 8, Ala at 15, Leu at 27 — that confer protease resistance and block dipeptidylpeptidase-IV cleavage [2]. At the level of receptor pharmacology, they are the same agonist.
Where they diverge is duration, and duration is decided entirely by the albumin handle. The DAC variant's maleimidopropionyl linker bonds to serum albumin and stretches the half-life into the 5.8-to-8.1-day range measured in humans [1]; the no-DAC form has no such linker and clears in the minutes-to-hours range of native GHRH(1-29) [1]. One feature — present or absent — separates a once-every-several-days kinetic profile from a same-day one. That is the entire pharmacokinetic story, and it is why a label that names only "CJC-1295" has not specified the molecule's most consequential property.
The functional consequence appears in the animal data too: once-daily dosing of the long-acting analog normalized growth in GHRH-knockout mice, while less frequent dosing was progressively inferior [4] — a result that only makes sense for a compound whose duration supports daily, not hourly, administration.
Reading a label or protocol honestly
Because the two forms are pharmacokinetically opposite, the variant designation is the first thing to verify in any claim. A multi-day duration belongs to the DAC conjugate; a same-day clearance belongs to the no-DAC form. A claim that mixes them — a multi-day effect attributed to "Modified GRF 1-29," or a short clearance attributed to "CJC-1295 DAC" — is internally inconsistent with the published pharmacokinetics [1].
Neither form is approved for human use, and the analytical literature underscores why precise identification matters: CJC-1295 was structurally confirmed by high-resolution LC-MS/MS as the active ingredient in an unknown "GHRH" preparation seized in an anti-doping context, because what a product is labeled and what it contains are not the same question [10]. This digest reports the pharmacology of each named form; it does not evaluate or endorse any product. The CJC-1295 half-life page rebuilds the kinetic timeline for each variant in full.