Growth Hormone Secretagogues: Mechanism Guide (2026)

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10 peptides in this class

CJC-1295

Target: GHRH receptor

CJC-1295 (also known as Mod GRF 1-29) is a modified GHRH analog with four amino acid substitutions that improve stability. With a short ~30 minute half-life, it mimics natural pulsatile GH release patterns. Often combined with GHRPs like Ipamorelin for synergistic effects.

CJC-1295 with DAC

CJC-1295 with DAC (Drug Affinity Complex) is a long-acting GHRH analog that binds to albumin, extending its half-life to 6-8 days. This allows for less frequent dosing compared to CJC-1295 without DAC, providing sustained GH elevation rather than pulsatile release.

GHRP-2

Target: GHSR-1a (ghrelin receptor)

GHRP-2 is a potent synthetic hexapeptide that stimulates growth hormone release through the ghrelin receptor (GHS-R). One of the strongest GHRPs available, it produces significant GH pulses with moderate effects on cortisol, prolactin, and appetite. Often stacked with GHRH peptides like CJC-1295 for synergistic effects.

GHRP-6

GHRP-6 is the original growth hormone releasing peptide, a synthetic hexapeptide that strongly stimulates GH release through the ghrelin receptor. Known for significant appetite stimulation (hunger effect within 20-30 minutes), making it popular for bulking phases and hardgainers who need to increase caloric intake.

Hexarelin

Hexarelin is one of the most potent GHRPs (Growth Hormone Releasing Peptides), producing strong GH pulses through the ghrelin receptor. More potent than GHRP-6 but with greater effects on cortisol and prolactin. Often used in research for its powerful GH-releasing properties.

IGF-1 LR3

Target: IGF-1 receptor

IGF-1 LR3 is a modified version of insulin-like growth factor 1 with an extended half-life (~20-30 hours vs minutes). The modifications make it more potent for muscle protein synthesis and less affected by IGF binding proteins. Used in research for muscle growth and recovery.

Ipamorelin

Ipamorelin is one of the mildest and most selective growth hormone releasing peptides (GHRPs). It stimulates GH release through the ghrelin receptor without significantly affecting cortisol or prolactin levels, making it popular for those seeking cleaner GH elevation with fewer side effects.

MK-677 (Ibutamoren)

Target: GHSR-1a (ghrelin receptor) — oral

MK-677 (Ibutamoren) is an oral growth hormone secretagogue that mimics ghrelin to stimulate GH and IGF-1 release. Unlike injectable peptides, it's taken orally and has a long duration of action. Known for increasing appetite, improving sleep, and supporting muscle/recovery.

Sermorelin

Sermorelin is the native GHRH(1-29) fragment — the first 29 amino acids of natural growth hormone-releasing hormone. It stimulates the pituitary gland to produce GH in a physiological, pulsatile pattern. The longest-studied GHRH analog with an established clinical track record.

Tesamorelin

Tesamorelin is the only FDA-approved GHRH analog — clinically shown to build lean muscle while reducing visceral belly fat by 15-18%. Uses the full 44 amino acid GHRH sequence with a trans-3-hexenoic acid modification for stability. Produces physiological GH pulses that drive both protein synthesis in skeletal muscle and lipolysis in abdominal fat.

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Helpful context for this guide

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Key takeaways

GHRP-6 acetate binds ghrelin receptors to trigger immediate GH release (peak 20–30 min) independent of hypothalamic signaling, while sermorelin amplifies only the natural GH pulses controlled by the hypothalamus.
Co-administration of GHRP-6 and sermorelin produces 3–5× greater GH peaks than either peptide alone due to convergent signaling through intracellular calcium and cAMP pathways.
GHRP-6 causes dose-dependent appetite stimulation (ghrelin mimicry) within 15–30 minutes; sermorelin does not affect appetite at all.
Sermorelin shows less receptor desensitization over extended protocols (12+ weeks) because it works within physiological feedback loops rather than overriding them.
Effective doses differ significantly: GHRP-6 typically 100–200 mcg per injection, sermorelin 200–500 mcg, with timing precision mattering far more for sermorelin.
Both peptides produce transient, self-limiting side effects (flushing, water retention) but avoid the severe metabolic disruption associated with exogenous recombinant GH.

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comparison

GHRP-6 vs Hexarelin: GH Secretagogue Comparison

GHRP-6 vs Hexarelin: GH Secretagogue Comparison GHRP-6 vs Hexarelin compared: potency, appetite stimulation, cardioprotective effects, dosing, evidence grades, and cost for GH secretagogue …

Source: pathtopeptides.comOpen reference →

comparison

Ipamorelin vs Other GHS Peptides

Ipamorelin Moderate Minimal High GHRP-2 Strong GHRP-6 Very strong Low Hexarelin Ipamorelin's high selectivity makes it particularly useful in studies where researchers want to isolate growt…

Source: regenpeptides.co.uk

Research context

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In Vivo Skeletal Research: Aged, OVX, and Somatopause Models

Aged C57BL/6 mice (18-24 months) represent the most translational model for ipamorelin bone research: somatopause (GH/IGF-1 decline with age) mirrors human ageing-associated GH secretory dysfunction and the resultant age-related bone loss. Ipamorelin (100-300 μg/kg s.c. twice daily × 8-16 weeks) in aged cohorts: primary endpoints — serum IGF-1 ELISA (confirming GH axis restoration), micro-CT distal femur trabecular (BV/TV, Tb.N, Tb.Th, Tb.Sp, Conn.D, SMI) and midshaft cortical (Ct.Th, Ct.TMD, J polar moment), dynamic histomorphometry (calcein 15 mg/kg day -14 + alizarin red 30 mg/kg day -7, undecalcified methylmethacrylate, MAR-BFR/BS-MS/BS), bone turnover serology (P1NP formation, CTX-I resorption), and 3-point bending biomechanics (Lloyd Instruments TA.XT, 10 mm span, 0.5 mm/s displacement, ultimate load, stiffness, toughness, post-yield displacement). Young adult (3-4 month) cohort run in parallel as the reference phenotype. OVX model (bilateral ovariectomy, 12-week C57BL/6 females): estrogen deficiency produces rapid trabecular bone loss (-40-50% BV/TV within 8 weeks). Ipamorelin treatment initiated at 8 weeks post-OVX (established osteoporosis), 4-week treatment phase (weeks 8-12). GH/IGF-1 axis restoration in the estrogen-deficient context: E2 normally potentiates hepatic GH receptor signalling via estrogen response elements in GHR and IGFBP-3 promoters — OVX reduces IGF-1 despite normal GH pulse frequency, positioning ipamorelin-driven GH pulse amplitude augmentation as a compensatory anabolic strategy. Zoledronic acid (100 μg/kg single i.v.) anti-resorptive comparator and teriparatide (40 μg/kg/day s.c.) anabolic comparator establish the pharmacological context for ipamorelin’s mechanism — with ipamorelin expected to increase both P1NP and modestly reduce CTX-I (contrasting with bisphosphonate-alone anti-resorptive profile).

Source: peptideslabuk.com ↗

Research Applications and Considerations

Ipamorelin metabolic syndrome research covers DIO visceral fat reduction via HSL/ATGL lipolysis, insulin sensitivity by ITT/GTT/GLUT4 translocation and hepatic IRS-2-Akt-PEPCK, dyslipidaemia by TG/HDL/LDL/VLDL secretion and LPL activity, hypertension by tail-cuff BP and aortic eNOS-NO relaxation, and adipokine profile normalisation (adiponectin:leptin ratio). The cortisol selectivity advantage over GHRP-6/GHRP-2 is the key mechanistic differentiator for clean GH-axis MetS attribution. Key methodological considerations: pair-feeding controls for appetite effects on fat mass; include GHR-KO arms for mechanism confirmation; measure IGF-1 as surrogate of GH axis restoration; and document the pulsatile GH profile (serial 10 min blood sampling for 2h post-injection) to confirm pulsatile (physiological) rather than tonic GH delivery. 🇬🇧 UK Research Peptides: PeptidesLab UK supplies COA-verified Ipamorelin for research and laboratory use. View UK stock → William is a research analyst at Peptides Lab UK, specialising in research peptides, laboratory compounds, and sourcing standards for high-purity peptide products.