Peptides for muscle growth work through distinct pathways — some stimulate GH release, others directly activate IGF-1 receptors, and some remove the biological ceiling on muscle size by inhibiting myostatin. This guide covers each class with clinical evidence ratings.
GH Secretagogue Stack (Best Starting Point)
CJC-1295 + Ipamorelin is the most popular starting combination. CJC-1295 is a GHRH analog that extends the GH pulse; Ipamorelin is a selective GHRP that triggers that pulse without elevating cortisol. Together they produce physiological GH release 3-4x above baseline.
Typical protocol: CJC-1295 (without DAC) 100mcg + Ipamorelin 100-200mcg before bed, 5 days/week.
MK-677 (Ibutamoren): An orally active GH secretagogue — the only one that works as a pill. Produces sustained GH and IGF-1 elevation but also increases appetite significantly (sometimes useful for bulking protocols).
Direct IGF-1 Pathways
IGF-1 LR3: A long-acting IGF-1 analog that directly stimulates muscle protein synthesis independent of GH. More potent at driving hypertrophy than GH secretagogues because it bypasses the GH → IGF-1 conversion step.
IGF-1 DES: A truncated IGF-1 variant with 10x greater potency at the receptor level. Very short half-life makes it ideal for local injection into a specific muscle immediately post-workout.
MGF / PEG-MGF: A splice variant of IGF-1 released in response to mechanical damage. Activates muscle satellite cells. PEG-MGF extends the half-life from minutes to 24-72 hours.
Myostatin Inhibitors (Maximum Muscle Potential)
Follistatin-344 / FST-315: Inhibit myostatin and activin simultaneously, removing the biological ceiling on muscle mass. The most extreme category — animal studies show 200%+ muscle mass gains with supraphysiological doses. Human data is very limited.
ACE-031: Soluble activin receptor decoy. Phase 2 trials showed significant muscle mass increases in Duchenne muscular dystrophy. Discontinued due to side effects (epistaxis, telangiectasias).
Supporting Compounds
BPC-157 + TB-500 (healing stack): Accelerate recovery between training sessions, reducing the limiting factor of muscle repair time.
GHRP-6/GHRP-2: Older GH-releasing peptides. GHRP-6 increases appetite significantly (useful for bulking), GHRP-2 is cleaner but less potent than Ipamorelin.
Key Takeaways
For most researchers, the CJC-1295 + Ipamorelin stack is the appropriate starting point — it produces measurable GH elevation with a favorable safety profile. IGF-1 variants and follistatin are considerably more experimental and carry greater uncertainty regarding long-term effects.