GH Secretagogues (Ipamorelin, CJC-1295, Tesamorelin)

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Upward Index: 02 - Compounds & Molecules MOC | Literature Dossier: GH Secretagogues (Ipamorelin, CJC-1295, Tesamorelin) - References

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1. Pharmacodynamics & Mechanism of Action

Unlike exogenous recombinant human Growth Hormone (rhGH), which produces a supraphysiological square-wave elevation that suppresses endogenous pituitary somatotrophs via negative feedback and downregulates peripheral GH receptors, Growth Hormone Secretagogues (GHS) preserve natural pulsatile ultradian GH secretion and somatostatin feedback loops.

• Dual-Receptor Somatotroph Synergy:
  1. GHRH Analogs (Tesamorelin, CJC-1295 / Mod GRF 1-29, Sermorelin): Bind the pituitary GHRH receptor ($G_s$-coupled GPCR), activating adenylyl cyclase $\to$ cAMP $\to$ Protein Kinase A (PKA) to increase GH gene transcription and prime vesicles for release.
  2. Ghrelin Mimetics / GHRPs (Ipamorelin, Hexarelin, GHRP-2/6, MK-677): Bind the Growth Hormone Secretagogue Receptor 1a (GHS-R1a) ($G_{q/11}$-coupled GPCR), activating Phospholipase C (PLC) $\to {\text{IP}}_3\to$ intracellular ${\text{Ca}}^{2+}$ depolarization, while simultaneously antagonizing hypothalamic Somatostatin (GHIH).
  • Synergistic Multiplication: Co-administering a GHRH analog (CJC-1295 No DAC) with a selective GHS-R1a agonist (Ipamorelin) produces a $3\text{- to }5\text{-fold}$ supra-additive GH pulse compared to either peptide alone.
• Receptor Selectivity (Ipamorelin vs. Older GHRPs): First/second-generation GHRPs (GHRP-6, GHRP-2, Hexarelin) and oral MK-677 (Ibutamoren) cause significant off-target spikes in ACTH/Cortisol, Prolactin, and intense ghrelin hunger/insulin resistance. Ipamorelin (Aib-His-D-2-Nal-D-Phe-Lys-NH2) is a selective pentapeptide that stimulates GH release with zero elevation of ACTH, cortisol, aldosterone, or prolactin even at $100\times$ the ${\text{ED}}_{50}$ dose.
• Tesamorelin (${\text{trans-3-hexenoyl-GHRH}}_{(1\text{–}44)}$): FDA-approved 44-amino-acid stabilized GHRH analog resistant to DPP-4 cleavage; selectively mobilizes Visceral Adipose Tissue (VAT) and hepatic fat by $-15\text{ to }-20\%$ via hormone-sensitive lipase activation without perturbing subcutaneous fat or glycemic control to the degree of rhGH.

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2. Pharmacokinetics & DAC vs. No-DAC Architecture

Compound	Receptor Class	Plasma $t_{1/2}$	Pulse Profile	Off-Target Hormone Bleed
Mod GRF 1-29 (CJC-1295 No DAC)	GHRH-R	$\sim 30\text{ minutes}$	Biomimetic sharp pulse (mimics natural nocturnal SWS GH peak)	None
CJC-1295 with DAC	GHRH-R (albumin-bound via Drug Affinity Complex)	$6\text{–}8\text{ days}$	Continuous “GH bleed” (non-physiological basal elevation; risks pituitary exhaustion)	Mild water retention
Ipamorelin	GHS-R1a (Ghrelin-R)	$\sim 2\text{ hours}$	Clean, saturable $2\text{–}3\text{ h}$ pulse	Zero cortisol or prolactin spike
Tesamorelin	GHRH-R (44-AA + hexenoyl cap)	$26\text{–}38\text{ minutes}$	Potent natural pulsatile GH & IGF-1 elevation ($+100\text{–}180\text{ ng/mL}$)	Minimal; preserves diurnal rhythm
MK-677 (Ibutamoren)	Oral non-peptide GHS-R1a	$24\text{ hours}$ (IGF-1 elevation)	Continuous 24h ghrelin receptor agonism (blunts insulin sensitivity via $\beta$-cell ghrelin signaling)	Elevates cortisol, prolactin, fasting glucose

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3. Dosing, Cycling & Synergies

• Standard Protocol:
  • Physiological Recovery & Sleep Stack: $100\text{–}200\mu \text{g}$ CJC-1295 (No DAC / Mod GRF 1-29) + $100\text{–}200\mu \text{g}$ Ipamorelin administered SubQ immediately before bed.
  • Visceral Fat & Cognitive Protocol: $1.0\text{–}2.0\text{ mg/day}$ Tesamorelin SubQ pre-sleep (optionally paired with $100\mu \text{g}$ Ipamorelin).
• Strict Prandial Timing Rule: Insulin and free fatty acids potently stimulate hypothalamic somatostatin, which blunts GHRH/GHRP-induced GH release by $>70\%$. Always administer $\ge 90\text{–}120\text{ minutes}$ after the last meal (zero carbohydrates or dietary fats before injection).
• Cycling Cadence: 5 days on / 2 days off, in 8- to 12-week cycles followed by a 4-week washout to maintain somatotroph receptor sensitivity.
• Synergies: Tissue Repair Peptides (BPC-157, TB-500, GHK-Cu) (BPC-157 upregulates tendon GH receptors by $7\times$ to capture the secretagogue GH pulse), Cholinergics (Alpha-GPC, Citicoline) (Alpha-GPC suppresses hypothalamic somatostatin), and AMPK & Glycemic Agents (Metformin, Berberine, Acarbose) (Berberine/Metformin counteracts GH-mediated hepatic gluconeogenesis).
• Contraindications & Biomarkers to Monitor:
  • Contraindications: Active malignancy or history of neoplasia (IGF-1 is mitogenic via IGF-1R/PI3K/Akt/mTOR), pre-existing insulin resistance / Type 2 Diabetes (monitor HbA1c), carpal tunnel syndrome, and WADA-tested sports (prohibited under S2).
  • Biomarkers: Serum IGF-1 (and Z-score) (target upper physiological quartile: $175\text{–}250\text{ ng/mL}$; avoid supraphysiological $>300\text{ ng/mL}$ for longevity), IGFBP-3, Fasting Insulin & Fasting Glucose (HOMA-IR), HbA1c, and DEXA Visceral Adipose Tissue (VAT) mass.

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4. Key Scientific Evidence Summary

• Tesamorelin Phase 3 Visceral Fat Trial: Falutz et al. (2007, NEJM; 2010, JCEM pooled analysis, $N=816$) demonstrated that $2\text{ mg/day}$ Tesamorelin reduced visceral adipose tissue (VAT) by $-15.2\%$ to $-18\%$ ($p<0.001$) and reduced triglycerides while preserving subcutaneous fat.
• Tesamorelin & Cognitive Function: Baker et al. (2012) published in Archives of Neurology ($N=152$) that 20 weeks of Tesamorelin significantly improved executive function and verbal memory in both healthy older adults and adults with Mild Cognitive Impairment ($p=0.003$), accompanied by elevated brain GABA and N-acetylaspartylglutamate (NAAG).
• Ipamorelin Receptor Selectivity: Raun et al. (1998) established in European Journal of Endocrinology that Ipamorelin is the first selective GHS-R1a agonist that releases GH with zero stimulation of ACTH or cortisol.

See full study breakdowns in GH Secretagogues (Ipamorelin, CJC-1295, Tesamorelin) - References.