Follistatin 315 vs Tirzepatide
Side-by-side comparison of key properties, dosing, and research.
Anabolic & IGF
Follistatin 315GLP-1 / Weight Loss Agonists
Tirzepatide- 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.
- Tirzepatide is an FDA-approved dual GIP/GLP-1 receptor agonist that produces greater weight loss than semaglutide in head-to-head trials. SURMOUNT-1 trial showed average 21% body weight reduction at 72 weeks at the highest dose. Marketed as Mounjaro (diabetes) and Zepbound (obesity).
- Half-Life
- ~3–5 hours (longer systemic circulation vs FST-344)
- ~5 days
- Admin Route
- SubQ, IM
- SubQ
- Research
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- Typical Dose
- No established human dosing protocol
- 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg
- Frequency
- Research use only
- Once weekly, subcutaneous
- 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
- Average 21% body weight reduction at highest dose (SURMOUNT-1)
- Superior to semaglutide in head-to-head SURPASS trials
- Dual GIP/GLP-1 mechanism for enhanced metabolic control
- Significant reduction in HbA1c for type 2 diabetes
- Improved cardiovascular risk markers
- Reduces visceral fat preferentially
- FDA-approved for T2DM (Mounjaro) and obesity (Zepbound)
- Weekly dosing
- 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 (most common during titration)
- Vomiting
- Diarrhea or constipation
- Abdominal pain
- +3 more
- Stacks With
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