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Overview
What is Follistatin 344?
Follistatin 344 (FS-344) is a naturally occurring glycoprotein that inhibits myostatin and activin A, members of the TGF-β superfamily that suppress muscle growth. The FS-344 gene encodes a 344-amino acid precursor that is cleaved to produce the circulating FS-315 isoform. Gene therapy studies in primates and human clinical trials for muscular dystrophy have demonstrated significant muscle hypertrophy and strength gains. However, injectable peptide use has very limited human data, a short half-life (~90 minutes), and most research involves gene delivery rather than exogenous peptide administration. Follistatin has been banned by WADA since 2019.
Key Benefits
Myostatin and activin A inhibition, potential muscle growth enhancement, studied for muscular dystrophy therapy
Mechanism of Action
Binds and neutralizes myostatin and activin A, preventing their interaction with ActRIIB receptors on muscle cells. This blocks TGF-β signaling that normally suppresses muscle growth, allowing enhanced hypertrophy.
Molecular Information
Weight
~37,800 Da (FS-315 mature form)
Length
344 amino acids (precursor); 315 amino acids (circulating form)
Type
Glycoprotein with follistatin domains
Amino Acid Sequence:
Full sequence available in UniProt P19883
* FS-344 precursor cleaved to FS-315, which includes C-terminal acidic tail that reduces cell surface binding
Pharmacokinetics
Research Indications
Myostatin Inhibition
Blocks myostatin from binding to muscle cell receptors, removing natural growth suppression
Activin A Blockade
Also inhibits activin A, providing dual-action anti-catabolic effect greater than myostatin-only inhibitors
Satellite Cell Activation
Research suggests follistatin may directly promote satellite cell proliferation for muscle regeneration
Research Protocols
Disclaimer
Most follistatin research involves gene therapy (AAV vector delivery) providing sustained expression for months. Injectable peptide has ~90-minute half-life and very limited human data. Results from gene therapy studies should not be extrapolated to injectable peptide use. This is not medical advice. Consult a healthcare provider before use.
Timing
No established optimal timing. Short half-life (~90 min) means effects may not persist between daily doses.
Peptide Interactions
How to Reconstitute
Important
Large glycoprotein (~38 kDa) - handle gently. Use sterile water or BAC water. Never shake vigorously as protein may denature. Store lyophilized at -20°C. Reconstituted solution is fragile - use within 7 days and keep refrigerated at 2-8°C.
Store lyophilized powder at -20°C until use
Add sterile/bacteriostatic water slowly down vial side
Gently swirl - do not shake vigorously as protein may denature
Solution should be clear - discard if cloudy
Use reconstituted solution within 7 days
Store reconstituted solution at 2-8°C, never freeze
Quality Indicators
Extremely limited human peptide data
Most research involves gene therapy, not injectable peptide. Efficacy and safety of subcutaneous peptide poorly established.
Very short half-life (~90 minutes)
Native follistatin is rapidly cleared. Systemic muscle effects from daily injection are questionable without sustained release formulation.
WADA banned substance
Prohibited in sports since 2019. Subject to doping detection methods.
Excessive dosing risk
Case report of central serous chorioretinopathy (vision impairment) at 1mg single dose (10x typical). Never exceed 200mcg/day.
Third-party testing essential
Given limited regulation and high potential for counterfeit, COA verification is critical.
What to Expect
- Week 1-2: No reliable timeline established for injectable peptide use
- Week 2-4: Gene therapy studies showed measurable changes by week 8
- Important: Most dramatic results (15% muscle increase) are from gene therapy providing sustained expression, not short-acting injections
- Injectable peptide effects likely much more modest due to rapid clearance
Side Effects & Safety
- CRITICAL: Most safety data is from gene therapy, not injectable peptide
- Gene therapy trials showed no serious adverse events in BMD patients
- Potential FSH suppression - may affect reproductive function
- Minor LDL cholesterol increase reported (~8 mg/dL) in some subjects
- Theoretical concerns: bone density reduction, organ fibrosis with chronic TGF-β inhibition
- Case report of vision impairment at 10x dose - never exceed recommended amounts
- Not recommended for those with active cancer due to growth factor modulation
- Contraindicated in pregnancy - follistatin affects reproductive signaling
References
Follistatin Gene Delivery Enhances Muscle Growth in Nonhuman Primates (2009)
AAV1-FS344 injection into quadriceps produced 15% circumference increase at 8 weeks, persisting 15+ months. Muscle fiber diameter increased significantly (87.7 μm vs 65.5 μm control). No adverse effects on cardiac, reproductive, or organ systems.
View Study (opens in new tab) →Phase 1/2a Follistatin Gene Therapy for Becker Muscular Dystrophy (2015)
First human gene therapy trial. Patients showed 6-minute walk test improvements up to +125 meters. High-dose patients showed muscle fiber diameter increase (40→59 μm) and 35-43% reduction in fibrosis. No serious adverse events. Hormone levels remained normal.
View Study (opens in new tab) →Long-term Enhancement of Muscle Mass by Myostatin Inhibitors (2008)
Transgenic mice expressing high follistatin levels showed 194-327% muscle mass increase. FS-344 produced greatest effects among tested inhibitors. Effects persisted over 2 years without adverse events in animal models.
View Study (opens in new tab) →Quick Start Guide
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