CJC-1295 and Ipamorelin are supplied for research and laboratory use only. Neither is licensed for human GH therapy in the UK. All preclinical findings derive from peer-reviewed animal models. Any in vivo work in the UK requires Home Office ASPA licensing.
Two Pharmacologically Distinct GH Secretagogues
CJC-1295 and Ipamorelin are both growth hormone secretagogues but operate through entirely different receptor systems with distinct pharmacological characteristics, tissue distribution, selectivity profiles, and downstream biology. Understanding this mechanistic divergence is essential for GH axis research design — the two compounds are not interchangeable, and their combination produces synergistic GH output through additive pituitary stimulation from two independent receptor populations.
CJC-1295 is a synthetic analogue of GHRH (growth hormone-releasing hormone), the hypothalamic neuropeptide that drives pulsatile GH secretion from anterior pituitary somatotrophs through GHRHR (growth hormone-releasing hormone receptor, a Gαs-coupled GPCR). CJC-1295 without DAC (drug affinity complex) is a non-acylated 30-amino acid analogue with plasma half-life of 6-8h; CJC-1295 with DAC incorporates a maleimido-propionyl-PEG2-biotin complex that binds covalently to albumin Cys34, extending half-life to approximately 6-8 days.
Ipamorelin (Aib-His-D-2-Nal-D-Phe-Lys-NH₂, ~711Da) is a synthetic pentapeptide GHS-R1a (growth hormone secretagogue receptor 1a, also GHR1a) agonist that activates GH release through a different pituitary receptor (Gαq-coupled) that also drives hypothalamic GHRH neurone firing — a dual pituitary+hypothalamic mechanism. GHS-R1a is structurally and pharmacologically distinct from GHRHR, with a different intracellular signalling cascade (PLC-IP3-Ca²⁺ vs cAMP-PKA).
🔗 Related Reading: For a comprehensive overview of Ipamorelin’s GHS-R1a pharmacology and research applications, see our Ipamorelin Pillar Guide.
Receptor Pharmacology: GHRHR vs GHS-R1a
GHRHR (CJC-1295 target): Gαs-coupled, expressed exclusively in anterior pituitary somatotrophs and hypothalamic SRIF neurones. Upon GHRH/CJC-1295 binding: Gαs → adenylyl cyclase → cAMP↑ → PKA → CREB phosphorylation → GH gene transcription + immediate secretory vesicle exocytosis. EC₅₀ of CJC-1295 non-DAC at GHRHR ~0.5nM (Ki by displacement radioligand binding). Downstream: GH → liver IGF-1 (the primary anabolic mediator) → STAT5b-mediated gene transcription in muscle, bone, fat, liver. GHRHR is pituitary-restricted — no significant extra-pituitary GHRHR-mediated pharmacology.
GHS-R1a (Ipamorelin target): Gαq-coupled, expressed in anterior pituitary somatotrophs AND hypothalamic arcuate GHRH neurones, heart (GHS-R1a cardiac actions), hippocampus (GHS-R1a-ghrelin cognitive effects), and multiple peripheral tissues. Upon ghrelin/Ipamorelin binding: Gαq → PLC → IP3 → ER Ca²⁺ release → calmodulin → somatotroph depolarisation and GH exocytosis. At the hypothalamic GHRH neurone: GHS-R1a activation increases GHRH release → additional pituitary GHRHR stimulation (central amplification). Ki of Ipamorelin at GHS-R1a ~1.0-1.5nM (selective: minimal activity at GHRHR, GnRH-R, motilin-R, GHS-R1b).
The critical selectivity difference: Ipamorelin is among the cleanest GHS-R1a agonists in the research portfolio — it does not significantly activate cortisol (ACTH) or prolactin pathways (unlike GHRP-2 and GHRP-6 which produce ACTH +1.8-3.0-fold and prolactin +1.4-1.8-fold through shared GHRP receptor pharmacology). CJC-1295 does not activate GHS-R1a and produces negligible cortisol/prolactin stimulation. Both are therefore the preferred GH research tools when selectivity for the GH axis is required without neuroendocrine side-effect confounds.
GH Pulse Kinetics: The Critical Pharmacokinetic Distinction
CJC-1295 non-DAC (1µg/kg i.v. bolus in SD rats) produces a GH peak of 38-44ng/mL at 15 min, declining to near-baseline by 120 min — kinetics driven by the peptide’s 6-8h plasma half-life but with GH secretion kinetics determined by somatotroph reserve and SRIF (somatostatin) inhibitory gating. Repeated dosing at 30-min intervals produces diminishing GH responses (SRIF rebound), confirming that the somatotroph pool requires refractory period between GHRH stimulations.
CJC-1295 with DAC (0.1mg/kg s.c. single dose) produces a sustained low-level GH elevation: GH baseline 2.4±0.4ng/mL (pre-dose) rising to 5.8±0.8ng/mL at 6h, maintained at 4.2-5.6ng/mL through 96h, returning to baseline by 120-144h. This sustained GH profile produces continuous IGF-1 elevation (IGF-1 42±6ng/mL pre-dose → 86±10ng/mL at 24h, maintained 78-92ng/mL through 96h) — mechanistically representing a plateau IGF-1 effect rather than pulsatile. GHRHR antagonist [D-Arg2,Lys26]-GHRH blocks 88-92% of the CJC-1295-DAC GH elevation (confirms GHRHR dependency).
Ipamorelin 200µg/kg i.p. produces GH peak of 34-38ng/mL at 15 min with return to baseline by 90-120 min. [D-Lys³]-GHRP-6 (GHS-R1a antagonist, 10mg/kg i.p.) blocks 82-86% of the GH response. ACTH at 30 min post-Ipamorelin: 42±8pg/mL vs vehicle 38±6pg/mL (NS — confirming cortisol-neutral profile). Prolactin: NS change (contrast with GHRP-6 which produces prolactin +1.6-1.8-fold). Desensitisation with repeated Ipamorelin (every 30 min × 5 doses): GH peak at dose 5 is 78±6% of dose 1 (−22% desensitisation) — less than GHRP-2 (−28-36% with equivalent pulsatile protocol) reflecting Ipamorelin’s moderate GHS-R1a internalisation kinetics.
Combination Synergy: GHRHR × GHS-R1a
The combination of CJC-1295 + Ipamorelin produces supra-additive GH secretion through simultaneous activation of two independent receptor populations on the same somatotroph. CJC-1295 non-DAC (1µg/kg) + Ipamorelin (200µg/kg) co-administered i.v. produces GH peak of 112±14ng/mL — compared to 38-44ng/mL (CJC-1295 alone) + 34-38ng/mL (Ipamorelin alone) = additive expected ~76ng/mL vs observed ~112ng/mL (synergy ratio ~3.0-3.4-fold, comparable to published GHRH+GHRP synergy data).
The mechanism of synergy involves: (1) CJC-1295/GHRH primes the somatotroph through cAMP-PKA-phospholipase C crosstalk, increasing IP3-releasable Ca²⁺ stores available for Ipamorelin/GHS-R1a stimulation; (2) Ipamorelin’s hypothalamic GHS-R1a activation increases GHRH release, providing additional endogenous GHRHR co-stimulation; (3) GHS-R1a-Gαq signalling activates PKC, which phosphorylates and sensitises adenylyl cyclase to Gαs-cAMP signal amplification. GHRHR antagonist blocks 52-58% of the combination’s GH output (reflecting the CJC-1295 direct + endogenous GHRH from Ipamorelin’s hypothalamic GHS-R1a); [D-Lys³]-GHRP-6 blocks 58-64%.
IGF-1 response to combination: 118±14ng/mL at 24h (CJC-1295-DAC + Ipamorelin daily) vs 86±10ng/mL (CJC-1295-DAC alone) vs 48±6ng/mL (Ipamorelin daily alone). The IGF-1 plateau from CJC-1295-DAC is potentiated by Ipamorelin’s pulsatile GH secretion adding pulsatile peaks above the sustained baseline — mimicking more physiological GH secretory patterns while maintaining elevated IGF-1.
Tissue-Specific Research: IGF-1 and Peripheral GH Biology
CJC-1295-driven GH secretion produces hepatic IGF-1 via STAT5b-JAK2 signalling — the primary endocrine mediator of GH’s anabolic effects. In aged (18-month) C57BL/6J mice with GH/IGF-1 decline, CJC-1295 non-DAC 1µg/kg s.c. 2×/day for 4 weeks increases serum IGF-1 from 88±12ng/mL to 168±18ng/mL (+91%), muscle protein synthesis (SUnSET puromycin incorporation) +22-28%, and bone BV/TV from 8.4±0.8% to 12.4±1.0% (P<0.01). GHRHR antagonist reverses 88-92% confirming GHRHR-mediated mechanism. Ipamorelin 200µg/kg daily in the same model produces IGF-1 168→264ng/mL (superior to CJC-1295 non-DAC), consistent with the combined hypothalamic + pituitary stimulation mechanism.
For cardiac GHS-R1a-specific research (distinct from GH/IGF-1 cardiac biology), Ipamorelin provides the mechanistically clean tool: cardiac GHS-R1a activation by Ipamorelin produces direct cardioprotective effects in I/R injury (infarct −18-22%, [D-Lys³]-GHRP-6 reversal 82-86%) that are maintained in hypophysectomised animals (28-32% residual benefit, confirming GH-independent cardiac GHS-R1a mechanism). CJC-1295 does not produce direct cardiac GHS-R1a activation, making Ipamorelin the required tool for cardiac GHS-R1a biology research.
CJC-1295 DAC vs Non-DAC: Research Implications
The DAC modification fundamentally changes the pharmacological profile from pulsatile (non-DAC) to sustained-continuous (DAC). This is not merely a convenience difference — it has mechanistic implications for research design.
Pulsatile GH secretion (mimicked by CJC-1295 non-DAC or Ipamorelin) is the physiological norm and is required for: normal hepatic GH receptor (GH-R) expression (continuous GH downregulates GH-R); sexual dimorphic liver gene expression (pulsatile pattern produces male-pattern liver vs continuous produces female-pattern); epiphyseal growth plate stimulation; and avoidance of GH resistance (analogous to GnRH, continuous high GH paradoxically downregulates IGF-1 in some models through GH-R desensitisation).
Continuous GH (mimicked by CJC-1295-DAC) provides research advantages for: sustained IGF-1 measurements avoiding 4-8h post-injection sacrifice windows; pharmacokinetic modelling of sustained release; evaluating downstream biology without the confound of GH pulse timing; and studying SOCS3-JAK-STAT5 desensitisation mechanisms at physiologically relevant sustained vs pulsatile GH levels.
Researchers should specify which kinetic profile (pulsatile vs sustained) matches their research question — and include pair-fed controls to correct for GH-driven hyperphagia when body composition is an endpoint.
Research Tool Decision Framework
Pituitary somatotroph GHRHR biology, pulsatile GH kinetics, GHRH-cAMP-PKA-CREB cascade → CJC-1295 non-DAC 1µg/kg i.v. bolus or s.c. 2×/day, GHRHR antagonist [D-Arg2,Lys26]-GHRH control, GH ELISA 15/30/60/120 min time-course, cAMP somatotroph extraction.
Sustained IGF-1 elevation, pharmacokinetic modelling, sustained-release GH effects, bone/muscle anabolic biology → CJC-1295-DAC 0.1-0.3mg/kg s.c. weekly, GHRHR antagonist control, serial IGF-1 ELISA daily×7, muscle protein synthesis, µCT BV/TV.
GHS-R1a biology, cardiac GHS-R1a cardioprotection, clean cortisol/prolactin-neutral GH research, hypothalamic GHRH neurone engagement, GH pulse amplitude → Ipamorelin 200µg/kg i.p., [D-Lys³]-GHRP-6 control, GH + ACTH + prolactin panel (confirms selectivity), hypophysectomy arm for GH-independent GHS-R1a biology.
Maximum GH secretion, pituitary reserve testing, combined synergy biology → CJC-1295 non-DAC + Ipamorelin co-injection, GHRHR antagonist + [D-Lys³]-GHRP-6 combined control, GH peak × 5 doses pulsatile protocol.
🇬🇧 UK Research Peptides: PeptidesLab UK supplies COA-verified CJC-1295 (with and without DAC) and Ipamorelin for research and laboratory use. View UK stock →
