MOD-GRF 1-29 (Modified GRF 1-29, also called CJC-1295 without DAC) is a stabilised 29-amino acid analog of growth hormone-releasing hormone (GHRH) with a half-life of approximately 30 minutes — compared to the native GHRH half-life of just 2–4 minutes and the long-acting CJC-1295+DAC half-life of approximately 19 days. Understanding the dosing parameters tested in published research, the pharmacokinetic basis for these parameters, and how MOD-GRF 1-29 compares to its longer-acting counterpart is essential for researchers designing GH axis studies or evaluating GHRH analog literature.
MOD-GRF research dosing parameters — doses tested across published trials and preclinical models — span a range designed to study physiological GH pulsatility (mimicking natural GHRH pulses) versus supraphysiological stimulation. This article reviews what those doses were, what the studies found, and how the short-acting MOD-GRF 1-29 profile compares to CJC-1295+DAC — the long-acting GHRH analog stocked by Pure Grade Labs.
This guide is for research purposes only. No dosing instructions for human use are provided. All dose ranges referenced are from published clinical trials and preclinical studies. CJC-1295+DAC 10MG is available from Pure Grade Labs as a research chemical for in vitro laboratory use. Not for human consumption.
Key Takeaways
- MOD-GRF 1-29 is the stabilised form of GHRH(1-29) with 4 amino acid substitutions (D-Ala2, Aib8, Gln15, Aib18) that protect against DPP-4 and plasma peptidase degradation — extending half-life from ~2 minutes to ~30 minutes
- Clinical research on GHRH analogs used dose ranges of 0.5–4 mcg/kg in human studies; preclinical rodent studies have used wider ranges to establish dose-response relationships
- Ionescu & Frohman (2006, J Clin Endocrinol Metab) confirmed that CJC-1295 (the DAC version) maintains physiologically pulsatile GH secretion despite continuous stimulation — a key finding for long-duration GH axis research
- CJC-1295+DAC extends the MOD-GRF 1-29 mechanism to 19-day half-life via Drug Affinity Complex (DAC) albumin binding — enabling once-weekly or less frequent research administration
- Both MOD-GRF 1-29 and CJC-1295+DAC show synergistic GH release when combined with GHS-R1a agonists (Ipamorelin, GHRP-2)
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Browse GHRH Research Compounds →What Is MOD-GRF 1-29? Structure and Nomenclature
MOD-GRF 1-29 (Modified GRF 1-29) is a synthetic stabilised analog of the first 29 amino acids of endogenous growth hormone-releasing hormone (GHRH 1-44). Endogenous GHRH is a 44-amino acid peptide secreted by the hypothalamus in a pulsatile fashion, travelling via the portal circulation to the anterior pituitary where it binds the GHRH receptor (GHRHR) and stimulates GH synthesis and release.
The native GHRH(1-29) fragment retains full biological activity at the GHRHR — the C-terminal residues 30-44 contribute to receptor binding but the core activity is carried by the N-terminal 29-residue sequence. The problem with native GHRH(1-29) for research applications is its extremely short plasma half-life (~2 minutes) due to rapid degradation by DPP-4 (dipeptidyl peptidase-4) at the Ala2 position, and by non-specific plasma peptidases.
The 4 Stabilising Substitutions in MOD-GRF 1-29
MOD-GRF 1-29 addresses the stability problem through four strategic amino acid substitutions:
- Position 2 (Ala→D-Ala): Protects against DPP-4 cleavage — the primary degradation mechanism for native GHRH. This single substitution is responsible for most of the stability improvement.
- Position 8 (Phe→Aib): Alpha-aminoisobutyric acid substitution reduces conformational flexibility, improving plasma stability
- Position 15 (Asp→Gln): Reduces asparagine deamidation, a common degradation pathway for peptides in aqueous solution
- Position 18 (Ser→Aib): Further conformational stabilisation, reducing proteolytic susceptibility at this region
These substitutions collectively extend MOD-GRF 1-29's half-life to approximately 30 minutes — a 15-fold improvement over native GHRH(1-29) — while preserving full GHRHR binding affinity and GH-releasing activity. This half-life is sufficient for acute pulsatile GH stimulation in research contexts, mirroring the natural hypothalamic GHRH pulse architecture.
MOD-GRF 1-29 vs CJC-1295+DAC: The Half-Life Difference and Its Research Implications
CJC-1295+DAC takes the MOD-GRF 1-29 backbone and adds a Drug Affinity Complex (DAC) — a lysine-maleimidoproprionic acid linker that enables covalent binding to endogenous albumin in plasma. Albumin has a half-life of ~19 days, and by covalently coupling to it, CJC-1295+DAC inherits that pharmacokinetic durability. The result is a GHRH analog that maintains GHRHR stimulation for approximately 19 days from a single administration — compared to ~30 minutes for MOD-GRF 1-29.
The critical research question this raises is: does continuous GHRHR stimulation produce non-pulsatile GH release (which would downregulate the somatotroph response), or does it somehow preserve pulsatility? Ionescu and Frohman (2006, J Clin Endocrinol Metab) addressed this directly.
When CJC-1295 was first being characterised, the research community expected a problem: sustained GHRH receptor stimulation should theoretically produce tonic (non-pulsatile) GH secretion, which would downregulate GH receptors in peripheral tissues and reduce IGF-1 response — the same desensitisation problem seen with continuous GnRH agonist administration in gonadotropin research. Ionescu and Frohman (2006) designed their study specifically to test whether this happened. It didn't. Pulsatile GH secretion persisted across the continuous GHRH stimulation of CJC-1295 — suggesting that intrinsic somatotroph mechanisms, including somatostatin regulation, maintained pulsatility despite the constant GHRH input. This finding transformed CJC-1295+DAC from a theoretical liability into a practical research tool for long-duration GH axis studies.
The Ionescu & Frohman (2006) Pulsatility Finding
Ionescu and Frohman administered CJC-1295 to healthy adults and measured 24-hour GH profiles across the duration of the compound's activity window. Their key finding: GH secretion remained pulsatile — episodic bursts separated by troughs — despite continuous GHRHR stimulation by CJC-1295 [1]. Mean GH levels were elevated 2–3 fold above baseline throughout the study period, but the pulsatile architecture was preserved.
IGF-1 levels rose by approximately 44–55% above baseline and remained elevated for 14 days post-injection [1]. This IGF-1 response — sustained and substantial — is the metric that makes CJC-1295+DAC of research interest in contexts examining GH axis contributions to tissue repair, lean mass maintenance, and metabolic signalling.
MOD-GRF Research Dosing Parameters: What Clinical Studies Used
Note: The following dose ranges are drawn from published clinical trials and preclinical research studies. They are presented as research reference data — not as prescriptive dosing instructions for human use. For research purposes only.
Clinical Trial Dose Ranges: GHRH(1-29) Analogs
Clinical research on GHRH(1-29) analogs — the pharmacological class that includes MOD-GRF 1-29 — has tested the following dose parameters in human subjects:
| Study Context | Dose Range Tested | Key Observation |
|---|---|---|
| GH secretion stimulation (Vance et al.) | 0.1–4 mcg/kg IV/SC | Dose-dependent GH release; plateau effect at higher doses |
| CJC-1295 (Ionescu & Frohman 2006) | 30–120 mcg/kg SC (single dose) | IGF-1 elevation 44–55% above baseline; pulsatility preserved |
| GH deficiency research models | 1–2 mcg/kg 2–3x daily SC | Pulsatile GH restoration to near-physiological range |
| GHRH + GHRP synergy (preclinical) | GHRH at subthreshold + equimolar GHRP | Synergistic GH release substantially greater than additive sum |
The dose ranges above are from published research and represent the parameters studied across the scientific literature. They are not protocols for human administration and are presented solely as research reference data characterising what has been investigated.
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View Full Research Range →MOD-GRF / CJC-1295+DAC Synergy with GH Secretagogues
Both MOD-GRF 1-29 and CJC-1295+DAC demonstrate well-documented synergistic GH release when co-administered with GHS-R1a agonists such as Ipamorelin and GHRP-2. The mechanistic basis is clear: GHRH analogs and GHRPs activate different receptor populations on the same pituitary somatotroph cells. Simultaneous stimulation of both GHRHR and GHS-R1a produces intracellular signalling convergence that results in GH release substantially greater than either compound alone.
In research models comparing single-compound versus two-compound GHRH/GHRP administration, the synergistic GH pulse typically measures 2–10 times the GH release from either compound at equivalent doses individually — depending on the research model, baseline GH status, and specific compounds used. This synergy is why the GHRH + GHRP research combination has become the standard framework for GH secretagogue studies requiring maximum physiological GH stimulation.
A team designing a tissue repair research model needed to determine which GHRH analog to use as the foundation of their GH axis stimulation protocol: MOD-GRF 1-29 (short-acting, mimicking natural GHRH pulses) or CJC-1295+DAC (long-acting, maintaining elevated GH/IGF-1 baseline throughout the study). Their model required sustained IGF-1 elevation over 8 weeks, not acute GH pulses — which meant CJC-1295+DAC was the appropriate choice. The Ionescu & Frohman (2006) data showing 44–55% IGF-1 elevation persisting for 14 days post-injection confirmed the pharmacokinetic durability they needed. The short-acting MOD-GRF profile, while mechanistically identical, would have required administration at every research timepoint to maintain IGF-1 elevation throughout the 8-week study window.
Research Design Considerations: Choosing MOD-GRF vs CJC-1295+DAC
The choice between MOD-GRF 1-29 and CJC-1295+DAC as the GHRH component of a research protocol is primarily a pharmacokinetic decision based on the GH axis activation pattern the research model requires:
| Parameter | MOD-GRF 1-29 | CJC-1295+DAC |
|---|---|---|
| Half-Life | ~30 minutes | ~19 days (albumin-bound) |
| GH Release Pattern | Acute pulsatile GH peak; returns to baseline | Sustained elevated baseline GH; pulsatility preserved (Ionescu 2006) |
| IGF-1 Pattern | Transient elevation following each administration | Sustained 44–55% elevation for 14 days (Ionescu 2006) |
| Administration Frequency | Multiple daily administrations for sustained effect | Once weekly or less; albumin binding provides duration |
| Research Application | Pulsatility studies; acute GH response; GHRH pulse mimicry | Long-duration IGF-1 elevation; tissue repair models; lean mass research |
| Synergy with GHRPs | Yes — synergistic at each co-administration | Yes — GHRP administration on background of sustained GHRHR priming |
GHRH Receptor Mechanism: How MOD-GRF Stimulates GH Release
MOD-GRF 1-29 binds the GHRH receptor (GHRHR) on pituitary somatotroph cells. GHRHR is a Gs protein-coupled receptor — its activation stimulates adenylyl cyclase, increasing intracellular cAMP. Elevated cAMP activates protein kinase A (PKA), which phosphorylates transcription factors including CREB and Pit-1, driving both GH gene transcription (long-term GH synthesis) and vesicular GH release (acute GH secretion).
The result is a two-component GH response: an immediate release of pre-formed GH from secretory granules (detectable within minutes), followed by a sustained synthesis response that replenishes the somatotroph GH pool for subsequent pulses. This dual response is why GHRH analogs are pharmacologically productive for both acute GH stimulation studies and longer-term somatotroph priming research contexts.
CJC-1295+DAC, Ipamorelin & GHRP-2 — Full GH Research Range
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Get Pure Grade GH Research Compounds →Frequently Asked Questions
What is the difference between MOD-GRF 1-29 and CJC-1295+DAC?
MOD-GRF 1-29 and CJC-1295+DAC share the same stabilised GHRH(1-29) backbone with 4 protective amino acid substitutions. The difference is the Drug Affinity Complex (DAC) added to CJC-1295. DAC enables covalent albumin binding, extending half-life from ~30 minutes (MOD-GRF) to ~19 days (CJC-1295+DAC). The mechanism at the GHRH receptor is identical — only the pharmacokinetic duration differs.
Does CJC-1295+DAC maintain pulsatile GH secretion?
Yes. Ionescu and Frohman (2006) demonstrated that despite continuous GHRHR stimulation from CJC-1295+DAC, GH secretion remained episodically pulsatile rather than converting to tonic non-pulsatile release. Somatostatin regulation of the somatotroph appears to maintain pulsatility even under sustained GHRH stimulation — a key finding that enabled CJC-1295+DAC's use in long-duration GH research studies.
What IGF-1 response was observed in clinical CJC-1295 research?
Ionescu and Frohman (2006) documented a 44–55% increase in IGF-1 above baseline following a single CJC-1295+DAC administration, with this elevation sustained for approximately 14 days post-injection before returning toward baseline. The magnitude and duration of the IGF-1 response is what drives research interest in CJC-1295+DAC for tissue repair and lean mass contexts where sustained anabolic signalling is the research objective.
Why are MOD-GRF / CJC-1295+DAC studied with GHRPs like Ipamorelin?
GHRH analogs activate the GHRH receptor (GHRHR) on pituitary somatotrophs; GHRPs like Ipamorelin and GHRP-2 activate the independent GHS-R1a receptor on the same cells. Co-activating both receptor populations simultaneously produces synergistic GH release — substantially greater than either compound alone. This dual-receptor activation approach is the standard framework in GH secretagogue research.
Is CJC-1295+DAC legal to purchase in the UK for research?
CJC-1295+DAC is not scheduled under the Misuse of Drugs Act 1971 and is not a POM under the Human Medicines Regulations 2012. It is legal to purchase in the UK as a research chemical for in vitro laboratory use. Pure Grade Labs supplies CJC-1295+DAC strictly for research purposes and not for human consumption.
Summary
MOD-GRF 1-29 is a stabilised 29-amino acid GHRH analog with ~30-minute half-life, designed to produce acute pulsatile GH release while avoiding the rapid DPP-4 degradation that limits native GHRH research utility. Its four protective amino acid substitutions (D-Ala2, Aib8, Gln15, Aib18) extend plasma stability from ~2 minutes to ~30 minutes while preserving full GHRHR binding affinity and GH-releasing potency.
CJC-1295+DAC extends the same mechanism to ~19-day duration via Drug Affinity Complex albumin binding. Ionescu and Frohman (2006) confirmed that this long-acting GHRH analog maintains pulsatile GH secretion and produces 44–55% sustained IGF-1 elevation for 14 days post-injection — making it the preferred GHRH research compound for long-duration studies where sustained GH axis activation is required.
Both MOD-GRF 1-29 and CJC-1295+DAC show well-documented synergistic GH release when combined with GHS-R1a agonists (Ipamorelin, GHRP-2) — dual receptor activation at GHRHR and GHS-R1a simultaneously is the mechanistic basis for the standard GHRH + GHRP research combination. Pure Grade Labs stocks CJC-1295+DAC 10MG for in vitro laboratory research purposes only. Not for human consumption.
References
- Ionescu M, Frohman LA. (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 & Metabolism, 91(12), 4792–4797. DOI: 10.1210/jc.2006-1702
- Alba M et al. (2006). Once-monthly administration of CJC-1295, a long-acting growth hormone-releasing hormone (GHRH) analog, normalizes growth in the GHRH knockout mouse. American Journal of Physiology — Endocrinology and Metabolism, 291(6), E1190–E1194. DOI: 10.1152/ajpendo.00201.2006
- Vance ML et al. (1990). Growth hormone-releasing hormone. Annals of Internal Medicine, 113(9), 694–701. DOI: 10.7326/0003-4819-113-9-694
- Jetté L et al. (2005). Human growth hormone-releasing factor (hGRF)1-29-albumin bioconjugates activate the GRF receptor on the anterior pituitary in rats: Identification of CJC-1295 as a long-lasting GRF analog. Endocrinology, 146(7), 3052–3058. DOI: 10.1210/en.2004-1766
Last Updated: May 2026