# CJC-1295 Research: Mechanism, Human Trials, and Structural Comparisons

> CJC-1295 activates pituitary GHRH receptors via a Gαs/cAMP/PKA cascade; in two human RCTs GH rose 2–10-fold and IGF-1 elevated for 9–11 days. This page covers mechanism, the DAC vs no-DAC distinction, and comparison with sermorelin.

## Mechanism of Action: GHRH Receptor Signaling

CJC-1295 binds the GHRH receptor (GHRH-R), a Gαs-coupled receptor expressed on anterior pituitary somatotroph cells. Binding activates adenylyl cyclase, elevating intracellular cAMP, which activates protein kinase A (PKA). PKA phosphorylates the transcription factor CREB, driving GH and GHRH-R gene expression; separately, PKA triggers voltage-dependent calcium-channel opening for acute GH exocytosis. MAPK and PI3K signaling pathways downstream mediate somatotroph proliferation [12].

This cascade is the shared mechanism of all GHRH analogs, including sermorelin and tesamorelin. CJC-1295 gains metabolic stability from four amino-acid substitutions (critically, Ala2 → Aib, blocking DPP-IV cleavage), extending plasma half-life from sermorelin's ~10–12 minutes to CJC-1295 no-DAC's ~30 minutes [15]. The DAC form extends this to 5.8–8.1 days [3].

CJC-1295 acts exclusively on the GH/IGF-1 axis. No direct testosterone effect has been demonstrated in published CJC-1295 trials [19].

## Human Clinical Evidence: The Two Published RCTs

Two randomized, placebo-controlled, double-blind trials constitute the complete published human evidence base for CJC-1295.

**Teichman et al. (2006)** enrolled healthy adult volunteers in an ascending-dose design (30, 60, 90, and 125 μg/kg SC). A single injection elevated mean plasma GH 2- to 10-fold dose-dependently, sustained for six days or more; IGF-1 rose 1.5- to 3-fold and remained elevated for nine to eleven days. Terminal half-life estimated at 5.8–8.1 days. No serious adverse reactions reported. Maximum trial duration: 49 days [1].

**Ionescu and Frohman (2006)** examined whether continuous GHRH-R stimulation would suppress endogenous GH pulsatility. At 60 and 90 μg/kg SC, trough GH rose 7.5-fold above baseline (P<0.0001) and mean GH rose 46%, but pulse frequency and amplitude remained intact — endogenous GH pulsatility was preserved [2].

Total enrolled n across both studies: 24. Maximum trial duration: 49 days. No long-term (>3 months) human safety data exists.

In GHRH-knockout mice, once-daily CJC-1295 at 2 μg/day SC over five weeks normalized body weight, tibial length, and GH mRNA levels [4].

## CJC-1295 with DAC: Drug Affinity Complex

The DAC (Drug Affinity Complex) is a proprietary C-terminal extension on CJC-1295 that includes a maleimide-reactive group. After subcutaneous injection, it forms a covalent thioether bond with Cys34 on circulating serum albumin. The resulting ~70 kDa complex is too large for renal filtration and shielded from proteolysis. Terminal half-life: 5.8–8.1 days [1]. The albumin bioconjugate produced a 4-fold increase in GH AUC over two hours versus unconjugated hGRF(1-29) in rats, and was detectable in plasma at 72 hours [3].

## Mod GRF 1-29: CJC-1295 Without DAC

Mod GRF 1-29 is the no-DAC version of CJC-1295. Market names 'CJC-1295 no DAC,' 'Modified GRF 1-29,' and 'Mod GRF 1-29' refer to the same molecule. Without the DAC extension, plasma half-life is approximately 30 minutes [15]. No published human pharmacokinetic study exists specifically for Mod GRF 1-29.

## CJC-1295 vs Sermorelin: Structural and Activity Differences

Sermorelin is a truncated native GHRH(1-29) analog with a half-life of ~10–12 minutes. CJC-1295 introduces four substitutions — most critically, Aib at position 2 — that resist DPP-IV inactivation and extend the no-DAC half-life to approximately 30 minutes [15]. No head-to-head clinical efficacy trial comparing sermorelin and CJC-1295 exists. Sermorelin has an FDA-approval history; CJC-1295 does not.

## CJC-1295 and Hormonal Axes

CJC-1295 acts on the GH/IGF-1 axis, not the HPG axis directly. No peer-reviewed study documents direct testosterone elevation from CJC-1295 administration [19].

## Oral Bioavailability

CJC-1295 has a molecular weight of approximately 3,647 Da. Peptides of this size are degraded by gastrointestinal proteases before reaching systemic circulation; no oral bioavailability has been documented [17]. All published studies use subcutaneous injection.

## CJC-1295 vs Exogenous HGH

CJC-1295 stimulates endogenous GH production, preserving pulsatility and negative feedback [2, 18]. Exogenous synthetic GH bypasses this regulatory architecture. No head-to-head clinical efficacy trial comparing CJC-1295 with exogenous GH exists.

## References

[1] Teichman SL, et al. J Clin Endocrinol Metab. 2006;91(3):799-805. https://pubmed.ncbi.nlm.nih.gov/16352683/
[2] Ionescu M, Frohman LA. J Clin Endocrinol Metab. 2006;91(12):4792-7. https://pubmed.ncbi.nlm.nih.gov/17018654/
[3] Jetté L, et al. Endocrinology. 2005;146(7):3052-8. https://pubmed.ncbi.nlm.nih.gov/15817669/
[4] Alba M, et al. Am J Physiol Endocrinol Metab. 2006;291(6):E1290-4. https://pubmed.ncbi.nlm.nih.gov/16822960/
[9] Falutz J, et al. J Acquir Immune Defic Syndr. 2010;53(3):311-22. https://pubmed.ncbi.nlm.nih.gov/20101189/
[12] Halmos G, et al. Rev Endocr Metab Disord. 2025. https://pubmed.ncbi.nlm.nih.gov/39934495/
[15] Jetté L, et al. [Sermorelin half-life.] Endocrinology. 2005;146(7):3052-8. https://pubmed.ncbi.nlm.nih.gov/15817669/
[17] Jetté L, et al. [Oral bioavailability.] Endocrinology. 2005;146(7):3052-8. https://pubmed.ncbi.nlm.nih.gov/15817669/
[18] Ionescu M, Frohman LA. [GH suppression absence.] J Clin Endocrinol Metab. 2006;91(12):4792-7. https://pubmed.ncbi.nlm.nih.gov/17018654/
[19] Teichman SL, et al. [HPG axis not measured.] J Clin Endocrinol Metab. 2006;91(3):799-805. https://pubmed.ncbi.nlm.nih.gov/16352683/
[21] Various authors. Body composition outcomes of Tesamorelin. ScienceDirect (in press 2026). https://pubmed.ncbi.nlm.nih.gov/41545261/

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A letterpress monograph on the GHRH analog CJC-1295 — with-DAC and without, hand-set from the peer-reviewed record, no clinic, no counter.