THE 30-SECOND OVERVIEW
At a glance
Few peptide names cause more confusion than CJC-1295. Two different molecules circulate under it, one carrying a modification called DAC and one without, and the difference between them is not cosmetic. It changes how long the peptide survives in circulation by roughly three orders of magnitude, which in turn changes what kind of research each version suits.
Start with the shared backbone
Both versions are built on GHRH(1-29), the first 29 amino acids of human growth hormone-releasing hormone and the shortest fragment that retains full activity at the GHRH receptor. This is the same backbone sermorelin uses.
The version sold as CJC-1295 without DAC, often written as modified GRF(1-29), carries four amino acid substitutions on that backbone: D-alanine at position 2, glutamine at position 8, alanine at position 15, and leucine at position 27. Each substitution targets a known weakness of the native sequence. The D-alanine at position 2 in particular obstructs dipeptidyl peptidase-4, the enzyme that cleaves native GHRH within minutes of it entering plasma.
Those four substitutions buy real stability at the receptor, but the peptide is still a small, unprotected molecule that the kidneys filter and plasma enzymes chew through. Its functional life in circulation is measured in tens of minutes.
What DAC actually is
DAC stands for Drug Affinity Complex, and it is not an amino acid substitution. It is a reactive group, maleimidopropionic acid on a lysine linker, attached to the C-terminal end of the same modified peptide.
The maleimide group does one specific thing: shortly after injection it forms a covalent bond with cysteine-34 on serum albumin, the single free thiol on the most abundant protein in blood. From that moment the peptide is no longer a free 30-residue molecule. It is a passenger on a 66 kDa carrier protein that the kidney does not filter and that circulates for weeks.
Jetté and colleagues described this albumin bioconjugation approach in 2005, and Teichman and colleagues published the human pharmacokinetics in 2006: single injections of CJC-1295 with DAC produced elevated growth hormone and IGF-1 levels that persisted for up to 14 days, with a half-life reported around six to eight days. The unconjugated peptide cannot do anything like that.
Why the difference matters in research
The reason to care is not simply duration. It is the shape of the signal.
Growth hormone is released in pulses, and the pituitary's response to GHRH is regulated by somatostatin in a feedback loop. A short-lived GHRH analogue produces a discrete pulse and then clears, leaving the feedback system in charge. A long-lived one applies continuous pressure at the receptor. Ionescu and Frohman examined this directly in 2006 and found that pulsatile growth hormone secretion actually persisted during continuous CJC-1295 exposure, with pulses riding on an elevated baseline. The feedback system holds its shape, but the two versions still present it with very different inputs.
This is why the two molecules, despite sharing a backbone, tend to appear in different research contexts. Work that needs a defined, transient stimulus reaches for the unmodified peptide. Work interested in sustained elevation of the growth hormone axis uses the DAC version, because that is the only version that produces it.
The naming problem
The literature name CJC-1295 properly refers to the DAC-carrying molecule; that is the compound Teichman's group studied. The version without DAC predates the name and is more accurately called modified GRF(1-29) or tetrasubstituted GHRH(1-29). Vendors adopted "CJC-1295 without DAC" because the backbone is identical, and the label stuck.
When reading a study or a product page, the question to ask is always which molecule is meant. A half-life claim of days belongs exclusively to the DAC version. A claim about sharp, short GH pulses belongs to the unmodified peptide. Conflating them is the single most common error in secondary write-ups of this compound.
How this pairs with other compounds
CJC-1295 is frequently studied alongside ghrelin-receptor peptides such as ipamorelin, because the two act on entirely different receptors that converge on the same downstream release. That pairing is common enough that combined preparations exist, such as the CJC-1295 + Ipamorelin blend, and the two compounds get a direct comparison of their own in the next article in this series. The non-peptide ghrelin-receptor agonist in the same literature is MK-677, dosed orally as a liquid or tablet in the published trials.
For delivery-format research, the unconjugated backbone also appears in intranasal work, which is the format our CJC-1295 nasal spray supplies.
The takeaway
The two versions of CJC-1295 share a receptor, a backbone, and four stabilising substitutions. The DAC group, a single reactive attachment that welds the peptide to serum albumin, is the entire difference, and it moves the compound's circulating life from around half an hour to the better part of a week. Neither version is a stronger form of the other. They are tools with different time courses, and published protocols choose between them on exactly that basis.
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References
1. Teichman, S. L., Neale, A., Lawrence, B., et al. (2006). 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. Journal of Clinical Endocrinology and Metabolism, 91(3), 799-805.
2. Jetté, L., Léger, R., Thibaudeau, K., et al. (2005). Human growth hormone-releasing factor (hGRF)1-29-albumin bioconjugates activate the GRF receptor on the anterior pituitary in rats. Endocrinology, 146(7), 3052-3058.
3. Ionescu, M., & Frohman, L. A. (2006). Pulsatile secretion of growth hormone (GH) persists during continuous stimulation by CJC-1295, a long-acting GH-releasing hormone analog. Journal of Clinical Endocrinology and Metabolism, 91(12), 4792-4797.
