DUAL CHANNEL · VARIANT COMPARE
CJC-1295 DAC vs No-DAC: The Pharmacokinetic Distinction
Two channels, one peptide backbone. The DAC variant tethers to serum albumin for a multi-day half-life; the no-DAC form is short-acting. The conflation that marketing exploits, drawn apart.
The CJC-1295 DAC vs no DAC Difference in One Line
CJC-1295 DAC vs no DAC comes down to a single structural feature: whether the peptide carries the albumin-binding moiety. Both forms share the same tetrasubstituted hGRF(1-29) backbone — D-Ala at position 2, Gln at 8, Ala at 15, Leu at 27 — that blocks dipeptidylpeptidase-IV cleavage, deamidation, and oxidation. The DAC ('Drug Affinity Complex') variant adds one more thing: a maleimidopropionyl linker on a C-terminal lysine that covalently binds the Cys34 thiol of circulating serum albumin.
That single addition is the entire pharmacokinetic story. The DAC variant's plasma half-life was estimated at 5.8 to 8.1 days in healthy adults [1]; the no-DAC form, lacking the albumin tether, clears on the timescale of native GHRH(1-29) — minutes to hours. Same receptor, same backbone, radically different duration.
CJC-1295 With DAC
CJC-1295 with DAC is the same tetrasubstituted GHRH(1-29) peptide plus the albumin-binding DAC moiety — and that moiety is what converts it from a short-acting peptide into a multi-day-acting one. The albumin-binding mechanism works by Michael addition: the maleimide linker reacts with the free thiol on Cys34 of serum albumin, forming a covalent peptide-albumin conjugate. Because the effective circulating species is now the much larger peptide-albumin complex (roughly 66 kDa), renal clearance slows dramatically and the molecule's residence approaches that of albumin itself.
The rodent data confirmed the design: the albumin conjugate was detectable in plasma beyond 72 hours and showed a 4-fold GH AUC increase over the unconjugated peptide [2]. In humans, the multi-day half-life and the up-to-28-day IGF-1 elevation after multiple doses followed directly from this chemistry [1].
Modified GRF 1-29 (the no-DAC form)
Modified GRF 1-29 is the common name for the no-DAC variant: the four-substitution hGRF(1-29) sequence without the albumin-binding handle. The substitutions still confer protease resistance — incorporating D-Ala at position 2 markedly increases the half-life and potency of GHRH(1-29)-NH2 by resisting DPP-IV cleavage [9] — but without the DAC tether, that resistance only stretches a minutes-scale peptide into a slightly longer minutes-to-hours window.
The practical consequence is that Modified GRF 1-29 and CJC-1295 DAC behave nothing alike in time. Marketing and forums routinely use the names interchangeably; the published pharmacokinetics do not support that. One is a once-weekly-scale molecule by design; the other is short-acting and would require frequent dosing to sustain any stimulus.
The Shared Backbone, Read Position by Position
Both variants are tetrasubstituted hGRF(1-29). The four substitutions — D-Ala at position 2, Gln at 8, Ala at 15, Leu at 27 — were chosen to stabilize the peptide's alpha-helix and to block the chemical liabilities of the native fragment: DPP-IV cleavage, deamidation, and oxidation. The most consequential single change is at position 2, where D-Ala blocks the dipeptidylpeptidase-IV cut that destroys native GHRH within minutes; that substitution alone markedly increases the half-life and potency of GHRH(1-29)-NH2 [9].
What the no-DAC form does not have is the C-terminal handle. In the DAC variant, a lysine near the C-terminus is functionalized with the maleimidopropionyl linker that does the albumin chemistry. Remove that handle and every other feature stays identical — same receptor affinity, same protease resistance, same sequence — but the molecule reverts to a free peptide. The entire DAC-vs-no-DAC difference is one terminal modification doing one job: keeping the peptide in circulation.
Why the Conflation Matters
The conflation is not pedantic — it changes what the data mean. When a forum cites the 5.8-8.1 day half-life [1] for a product that is actually no-DAC Modified GRF 1-29, the figure is simply wrong for that molecule. The two variants were validated in different ways: the DAC kinetics rest on the human PK studies that used 30 to 90 micrograms/kg subcutaneously [1] [3], while the no-DAC form's behavior follows from native GHRH(1-29) clearance with the protease-resistant substitutions.
The dosing consequence is concrete. A multi-day molecule and a minutes-to-hours molecule cannot share a schedule: what sustains a stimulus for one would barely register for the other. The GHRH-knockout mouse work showed how sharply interval matters even for the long-acting form — once-daily normalized growth while 48- to 72-hour spacing did not [4] — and the no-DAC form's window is far shorter still.
This is also where the honest gaps live. There is no large human efficacy or long-term safety trial for either form, and the original long-acting DAC program (ConjuChem) was discontinued; a Phase 2 trial in HIV-associated visceral obesity did not advance the DAC program [1]. The chemistry is well characterized; the long-term human picture is not, for either channel.