DAC, No-DAC, Mod GRF: GH Peptide Jargon Decoded

Few corners of the peptide world are as cluttered with confusing labels as the growth-hormone-releasing family: GHRH, GRF (1-29), Mod GRF 1-29, sermorelin, CJC-1295, and the ever-present suffix debate — with DAC versus no-DAC. Much of the confusion is that several of these names point at the same molecule, and the differences that do exist come down to two small chemical ideas. This piece decodes the jargon; for the rest of the growth-hormone-peptide terminology, keep the peptide research glossary open alongside it.

Start with the parent molecule: GHRH

GHRH is growth-hormone-releasing hormone — a natural hormone your hypothalamus makes that tells the pituitary to release growth hormone (GH). The full hormone is 44 amino acids long, but the biologically active business end is the first 29, written GRF (1-29) (“growth-hormone-releasing factor, residues 1 through 29”). Every peptide in this article is a variation on that 29-amino-acid fragment.

The problem with plain GRF (1-29) is speed. In the bloodstream it is chewed apart by an enzyme called dipeptidyl peptidase-4 (DPP-4), which snips the peptide between its 2nd and 3rd amino acids — incubated in plasma, the main breakdown product that shows up is GRF(3-29), the molecule minus its first two residues. The result is a half-life measured in minutes. In one human infusion study GHRH(1-29)-NH₂ disappeared with a half-time of 4.3 minutes; review literature puts sermorelin — which is essentially GRF (1-29) — at roughly 10 to 20 minutes in humans. Either way, minutes. Everything that follows is an attempt to solve that speed problem.

‘CJC-1295 no-DAC’ and ‘Modified GRF (1-29)’ are two names for the same thing: a GHRH fragment with four amino-acid swaps that resist rapid enzyme breakdown.

Fix #1: the four substitutions (Mod GRF 1-29 = CJC-1295 no-DAC)

The first fix is to make the peptide harder for DPP-4 to cut. Chemists swap four of the amino acids. Doping-control laboratories, which have to identify the molecule precisely, write it as (D-Ala², Gln⁸, Ala¹⁵, Leu²⁷)-GRF amide — substitutions at positions 2, 8, 15, and 27. The load-bearing one is position 2: putting D-alanine at that penultimate position blocks the exact bond DPP-4 tries to cleave. Swapping in alanine at position 15 also lengthened plasma survival in vitro, though only slightly — 13 minutes to 17 minutes in porcine plasma. What the position 8 and 27 swaps contribute is not something the literature I could open puts a number on.

Here is where the marketing runs ahead of the evidence. This “tetrasubstituted” GRF (1-29) is routinely described as lasting 30 minutes to a couple of hours. There is no published human pharmacokinetic study of it. The nearest human measurement is for a molecule carrying only the position-2 change: infused into ten normal men, D-Ala²-GHRH(1-29)-NH₂ disappeared with a half-time of 6.7 minutes, against 4.3 minutes for the unmodified peptide. A real improvement, statistically — and still minutes, not hours. Treat any specific half-life quoted for mod GRF 1-29 as unsourced until someone publishes one. This molecule goes by two interchangeable names:

• Modified GRF (1-29) (often “Mod GRF 1-29”)
• CJC-1295 without DAC (“CJC-1295 no-DAC”)

They are the same compound. If you understand that, half the naming confusion evaporates.

Fix #2: the DAC (CJC-1295 with DAC)

The second fix is far more dramatic and is the actual meaning of the DAC suffix. DAC stands for Drug Affinity Complex — a small reactive chemical group (a maleimidopropionamide on a C-terminal lysine) bolted onto the peptide. After injection, that group bioconjugates (chemically bonds) to serum albumin, latching onto the free thiol on cysteine-34 of the most abundant protein in your blood. Tethered to a large, long-lived carrier protein, the peptide is shielded from clearance and circulates for a very long time.

How long? The molecule carrying that DAC group is what’s specifically called CJC-1295 (with DAC), and unlike the no-DAC version it does have published human data: two randomised, placebo-controlled, double-blind ascending-dose trials in healthy adults aged 21–61, reported in 2006. Those studies estimated a half-life of 5.8 to 8.1 days — roughly a week — and reported that a single injection raised mean GH levels 2- to 10-fold for six days or more and IGF-1 1.5- to 3-fold for nine to eleven days. That is the entire reason the DAC version is discussed as a once-or-twice-weekly compound while the no-DAC version is discussed as a daily one.

The naming trap

Here’s the mess the market created: “CJC-1295” on its own is ambiguous. Technically, the name CJC-1295 refers to the DAC-bearing, week-long molecule. But it is routinely used loosely to mean the no-DAC (Modified GRF 1-29) version too. So “CJC-1295” with no suffix can point at either a compound that lasts an hour or one that lasts a week — a 100-fold difference in duration hiding behind one label. Always look for the suffix, and treat an unlabeled “CJC-1295” as under-specified. The practical trade-offs behind choosing one over the other are laid out in CJC-1295 no-DAC vs DAC — which and why.

Side-by-side

Name(s)	What it is	Half-life, and where the number comes from	Why
GHRH / GRF (1-29) / sermorelin	Native fragment, unmodified	4.3 min measured in men; ~10–20 min per review literature	Rapid DPP-4 cleavage between residues 2 and 3
Mod GRF 1-29 = CJC-1295 no-DAC	4 amino-acid substitutions	No published human study. 6.7 min for the D-Ala² analog in 10 men	D-Ala² blocks the DPP-4 cleavage site
CJC-1295 with DAC	Adds albumin-binding DAC group	5.8–8.1 days, measured in healthy adults	Tethers to cysteine-34 of serum albumin

Read down the table and the whole family is just one fragment with two escalating durability upgrades.

Why the “pulse vs plateau” idea comes up

Because the versions last such different lengths of time, they produce different shapes of GH signal, and you’ll see this framed as “pulsatile” versus “sustained.” A short-acting no-DAC peptide produces a brief, sharp rise that fades within hours; the DAC version keeps a low-level signal elevated for days. Proponents argue the short pulse more closely mimics the body’s natural rhythm, while others favor the convenience of the long-acting form. This distinction is central to why the compounds are often paired with a separate secretagogue like ipamorelin — the rationale, and its limits, are covered in CJC-1295 and ipamorelin: how the combo is supposed to work. The important caveat is that “mimics natural rhythm” is a mechanistic hypothesis, not a proven clinical advantage.

The honest bottom line

Strip away the jargon and this is a small, learnable vocabulary: GHRH/GRF (1-29) is the natural fragment; Mod GRF 1-29 and CJC-1295 no-DAC are the same four-substitution, hours-long version; CJC-1295 with DAC is the albumin-binding, week-long version. The suffix is the whole story, and an unlabeled “CJC-1295” tells you almost nothing.

Two honest limits. The pharmacology above is well characterized for the DAC compound (from a small early human study) but the benefits people actually seek — body composition, recovery, anti-aging — are not established by large, controlled human trials for any of these. And critically, these are research compounds that are largely not approved for human use. Decoding the names is educational; it is not a protocol, an endorsement, or medical advice. Keep the peptide research glossary as your reference, and take any health decision to a qualified clinician.

Sources

• Teichman SL, et al. “Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults.” J Clin Endocrinol Metab. 2006;91(3):799–805 (CJC-1295 with DAC half-life 5.8–8.1 days).
• “Modified GRF (1-29)” — Wikipedia (four substitutions at positions 2, 8, 15, 27; D-Ala at position 2; DPP-4 resistance; half-life comparison to sermorelin).