two companion daisies · one big difference
CJC-1295 DAC vs no DAC (Modified GRF 1-29): the half-life difference
One form lasts days; the other lasts minutes to hours. They share a backbone and get conflated constantly. Here is the difference, drawn plainly.
The whole story in one sentence
The CJC-1295 DAC vs no DAC question has one clean answer: the DAC form is covalently bound to your own serum albumin and lasts for days, while the no-DAC form is not bound to anything and lasts minutes to hours. Both share the same tetrasubstituted hGRF(1-29) backbone — the four protease-resistant substitutions are identical — so the only structural difference is the albumin-binding handle. But that one handle changes the pharmacokinetics by orders of magnitude [1].
Marketing and forums routinely treat "CJC-1295" and "Modified GRF 1-29" as interchangeable. They are not. Getting this wrong is the single most common error in the popular literature, which is why it gets its own page here.
What is CJC-1295 with DAC?
The DAC variant carries a maleimidopropionyl-lysine handle that covalently bonds to a thiol on circulating serum albumin (Cys34), forming a peptide-albumin conjugate that extends the plasma half-life toward that of albumin itself — hence a multi-day duration of action [2]. In healthy adults that translated to an estimated half-life of 5.8–8.1 days, with IGF-1 elevation persisting up to 28 days after multiple doses [1].
The engineering proof came from rats: the albumin-conjugated analog gave a ~4-fold higher growth-hormone area-under-the-curve over two hours than unconjugated hGRF(1-29) and stayed detectable in plasma beyond 72 hours [2]. This is the design that makes CJC-1295 long-acting.
What is CJC-1295 DAC?
"DAC" stands for Drug Affinity Complex — the albumin-conjugation chemistry, not a separate molecule. When people say "CJC-1295 DAC" they mean the version built to grab albumin and circulate for days. In the rat data, the conjugate produced roughly 4-fold higher growth-hormone AUC than the unconjugated peptide and was detectable beyond 72 hours [2]; that long residence is precisely what the DAC chemistry buys.
Modified GRF (1-29): The No-DAC Form
Modified GRF 1-29 is the no-DAC form: the same tetrasubstituted GHRH(1-29) sequence, with the four substitutions that block DPP-IV cleavage and stabilize the peptide, but without the albumin-binding DAC moiety [1]. Stripped of the albumin anchor, it clears on roughly the timescale of native GHRH(1-29) — minutes to hours rather than days.
That short action is sometimes presented as an advantage, on the logic that brief, pulse-like stimulation more closely mimics the body's own GHRH rhythm. Whether that matters clinically is not something the published human literature on Modified GRF 1-29 has tested. What is certain is the pharmacokinetic contrast: short-acting no-DAC versus multi-day DAC, the same fact every careful summary leads with.
Side by side
The two forms compared on the properties that actually differ:
| Property | CJC-1295 DAC | No-DAC (Modified GRF 1-29) | |---|---|---| | Albumin binding | Yes — covalent, via DAC handle [2] | No | | Estimated half-life | ~5.8–8.1 days [1] | Minutes to hours [1] | | Duration of GH/IGF-1 effect | IGF-1 elevated up to ~28 days after multiple doses [1] | Short, pulse-like [1] | | Backbone | Tetrasubstituted hGRF(1-29) [2] | Tetrasubstituted hGRF(1-29) [2] | | Route studied | Subcutaneous [1] | Subcutaneous [1] |
The backbone is the same; the half-life is not. Hold onto that and the rest of the literature reads cleanly.
How much CJC-1295 DAC should I take?
The DAC variant's multi-day half-life (5.8–8.1 days) was studied at single subcutaneous doses of 30–90 µg/kg in healthy adults [1], and murine work showed once-daily 2 µg normalized growth in GHRH-knockout mice [4]. Online fixed-microgram "protocols" are not derived from controlled human trials, and CJC-1295 has no approved human use. The doses that appear in studies are listed, with their context, on the doses used in the studies page.