CJC-1295 DAC vs No-DAC: The Pharmacokinetic Difference

CJC-1295 DAC vs no DAC: the one distinction that matters

The single most-conflated point in the CJC-1295 literature is the difference between CJC-1295 DAC vs no DAC. They share the same 29-residue backbone and the same four protease-resistant substitutions, but they behave on completely different timescales ^[3]. Treating them as interchangeable — which marketing and forums routinely do — gets the pharmacokinetics wrong by orders of magnitude ^[12].

CJC-1295 DAC has an estimated half-life of 5.8-8.1 days in healthy adults; a single subcutaneous dose elevates GH and IGF-1 for days, and IGF-1 stays above baseline up to 28 days after multiple doses ^[1]. The no-DAC form — 'Modified GRF 1-29' — keeps the substitutions but lacks the albumin-binding moiety, so it is short-acting, clearing on a minutes-to-hours scale. Same sequence at the core, radically different residence time.

The mechanism of the difference is one chemical handle, covered next. Everything that follows — the half-life numbers, the dosing interval, the choice of form — flows from whether that handle is present. The full citation set is on the full reference list.

What is CJC-1295 with DAC, and what is CJC-1295 DAC?

The DAC modification is a single, specific piece of chemistry, and the two questions readers most often ask about it have the same answer at their core.

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

'Modified GRF 1-29' is the tetrasubstituted GHRH(1-29) sequence without the DAC albumin handle. Reference material describes it as a synthetic GHRH analog carrying the same four stabilizing substitutions but lacking the albumin-binding moiety, and therefore with a much shorter duration of action than CJC-1295 DAC ^[11].

Functionally, the no-DAC form behaves close to native GHRH(1-29) with added protease resistance: it stimulates the same GHRH receptor, but it clears quickly, so its effect is a short pulse rather than a multi-day elevation. That is why dosing schedules for the no-DAC form differ from the DAC form — a point that drives most of the confusion in 'CJC-1295' discussions ^[12]. When a source quotes a frequent dosing schedule and short duration, it is almost always describing the no-DAC form; when it quotes a multi-day half-life, it is describing the DAC form ^[1].

Half-Life: DAC vs No-DAC

The half-life is the whole story of this distinction. CJC-1295 DAC has an estimated half-life of 5.8-8.1 days in healthy adults, with IGF-1 elevation persisting up to 28 days after multiple doses ^[1]. The no-DAC Modified GRF 1-29 form is short-acting — minutes-to-hours — reflecting native GHRH(1-29) clearance with the protease-resistant substitutions. The two differ not by a margin but by orders of magnitude.

The practical consequence is the dosing interval. In GHRH-knockout mice, once-daily 2-ug CJC-1295 DAC fully normalized growth, while less frequent dosing was progressively inferior ^[4] — a schedule that only makes sense for a multi-day-half-life molecule. A short-acting no-DAC peptide cannot hold the same sustained elevation; its exposure rises and falls within hours. When you read a half-life figure for 'CJC-1295', the form determines whether it means days or minutes, and a source that does not specify the form has not actually told you the half-life.

The chemistry of the difference, in one paragraph

Both forms start from the same tetrasubstituted hGRF(1-29) sequence — D-Ala at position 2, Gln at 8, Ala at 15, Leu at 27 — which is what makes either of them resistant to DPP-IV cleavage, deamidation, and oxidation ^[3]. That shared scaffold is why they have the same receptor target and the same immediate pharmacology. The divergence is one appended group: in the DAC form, a C-terminal lysine carries a maleimidopropionyl linker that bonds covalently to the Cys34 thiol of serum albumin, so the circulating species becomes a roughly 66-kDa peptide-albumin complex that clears at albumin's pace ^[3]. Remove that linker and you have the no-DAC Modified GRF 1-29, which clears at the peptide's own much faster pace ^[11]. One chemical handle is the entire pharmacokinetic story.

Registry sources, it should be noted, do not fully agree on CJC-1295's exact molecular formula: the CAS-registry consensus for the DAC variant is C152H252N44O42 (about 3367.9 Da before albumin conjugation), while PubChem lists a different formula. That kind of registry disagreement is exactly the sort of detail this site flags rather than smooths over.

Dosing schedules diverge because the half-life diverges

Because the DAC variant persists for days and the no-DAC form for minutes-to-hours, their research dosing schedules cannot be the same, and neither maps to an approved human protocol ^[1][12]. The GHRH-knockout-mouse work shows the long-acting form working on a once-daily schedule ^[4]; a short-acting no-DAC peptide would require a fundamentally different, more frequent pattern to approximate sustained exposure — and even then, that is a research observation, not a human protocol ^[12].