Follistatin 315 vs Retatrutide
Side-by-side comparison of key properties, dosing, and research.
Anabolic & IGF
Follistatin 315GLP-1 / Weight Loss Agonists
Retatrutide- Summary
- Follistatin 315 is a splice variant isoform of follistatin produced by alternative mRNA processing. Unlike Follistatin 344 which is tethered to cell surfaces via heparan sulfate proteoglycans, FST-315 circulates freely in the bloodstream and has broader systemic distribution. It is the predominant circulating form and exerts systemic myostatin inhibition as well as FSH suppression, making it relevant to both muscle growth and reproductive endocrinology.
- Retatrutide is an investigational triple receptor agonist targeting GLP-1, GIP, and glucagon receptors simultaneously. Phase 2 trials showed an unprecedented average 24% body weight reduction at 48 weeks — exceeding any approved medication to date. It is in Phase 3 trials as of 2024.
- Half-Life
- ~3–5 hours (longer systemic circulation vs FST-344)
- ~10–12 days
- Admin Route
- SubQ, IM
- SubQ
- Research
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- Typical Dose
- No established human dosing protocol
- 0.5 mg → 1 mg → 2 mg → 4 mg → 8 mg → 12 mg
- Frequency
- Research use only
- Once weekly
- Key Benefits
- Systemic myostatin inhibition for whole-body muscle growth
- Freely circulating — broader tissue distribution than FST-344
- Strong FSH-suppressive activity useful in certain hormonal protocols
- Potential for greater anabolic effect across multiple muscle groups simultaneously
- May be more relevant to reproductive endocrinology applications
- Studied in gene therapy approaches for muscular dystrophy
- ~24% body weight reduction at 48 weeks in Phase 2 (highest dose)
- Superior to both semaglutide and tirzepatide in early trial comparisons
- Triple receptor mechanism addresses multiple obesity pathways
- Significant reduction in liver fat (MASH/NAFLD indication being studied)
- Improved cardiovascular and metabolic markers
- Once-weekly dosing
- Potential for greatest weight loss of any currently investigated compound
- Side Effects
- Systemic FSH suppression — significant concern for fertility
- Greater potential for off-target effects vs FST-344 due to systemic distribution
- Limited human safety data
- Potential cardiac hypertrophy with prolonged high-dose exposure
- Nausea and vomiting (common during titration, similar to semaglutide/tirzepatide)
- Diarrhea
- Constipation
- Heart rate increase (from glucagon receptor agonism)
- +2 more
- Stacks With
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