Follistatin 344
A 344-amino-acid recombinant follistatin isoform that sequesters myostatin and activin A to release the natural brake on skeletal muscle growth.
Follistatin-344 is the predominant tissue-bound isoform of follistatin, a glycoprotein (~37 kDa) that binds and neutralizes TGF-beta superfamily members myostatin (GDF-8) and activin A, preventing them from signaling through skeletal muscle activin receptors and thereby relieving their inhibition of muscle protein synthesis and satellite cell activation. Transgenic and gene-therapy models show dramatic muscle hypertrophy, but there are no human clinical trials of the injectable recombinant protein at performance doses, no established pharmacokinetics, and well-documented quality problems in gray-market vials. It is not FDA-approved for any indication and is prohibited by WADA as a myostatin function modifier.
Class
Recombinant TGF-beta binding glycoprotein (follistatin FS-344 isoform, ~344 amino acids)
Half-life
Reported ~10-36 hours (estimated; no reliable human pharmacokinetic data exists for performance doses)
Routes
Intramuscular, Subcutaneous
Category
Growth Hormone & Performance
Researched benefits
What it's studied for
Dual TGF-beta inhibition (myostatin + activin A)
Follistatin-344 simultaneously binds and neutralizes myostatin and activin A, two complementary negative regulators of muscle growth, giving it a broader inhibition profile than agents that target only the myostatin pathway. This dual-pathway mechanism is the core rationale behind its performance interest.
Skeletal muscle hypertrophy (animal models)
Transgenic and viral gene-therapy models show large increases in lean muscle mass. Myostatin-null animals (the Belgian Blue cattle phenotype) and high-follistatin-expressing knockout mice show 2-3x normal muscle mass, establishing the theoretical ceiling of the pathway.
Satellite cell activation and protein synthesis
By removing myostatin signaling, satellite cells proliferate more aggressively, myoblast fusion is enhanced, and muscle protein synthesis exceeds catabolism, driving myofiber hypertrophy in preclinical work.
Muscular dystrophy research context
An AAV-delivered follistatin-344 gene therapy Phase 1/2a trial in Becker muscular dystrophy improved 6-minute walk distance in most patients with reduced fibrosis and increased fiber size, establishing proof-of-concept and initial safety data for the target (though via gene therapy, not injectable protein).
Fibrosis reduction and tissue remodeling
Follistatin's broad TGF-beta binding is researched for reducing fibrosis and supporting tissue remodeling; histology in the Becker MD trial showed reduced fibrosis alongside muscle growth.
Mechanism
How it works
Follistatin-344 is an activin-binding glycoprotein that binds and sequesters myostatin (GDF-8), the primary negative regulator of skeletal muscle mass. By preventing myostatin from engaging the activin type II receptor (ActRII), it blocks the downstream signaling cascade that normally suppresses muscle growth. Without myostatin signaling, satellite cells proliferate, myoblast fusion increases, and muscle protein synthesis outpaces catabolism.
Beyond myostatin, follistatin binds activin A, activin B, and GDF-11, broadening its inhibition across the TGF-beta superfamily. This is a double-edged property: the dual myostatin/activin A blockade is what distinguishes it from myostatin-specific agents, but the same broad binding regulates cell-cycle control across epithelia, liver, reproductive tissue, and cardiac muscle, raising off-target proliferation concerns. Marketing that calls it a selective myostatin antagonist mischaracterizes the biology.
The FS-344 isoform is the tissue/membrane-bound form (as opposed to circulating FS-315 and heparin-binding FS-288); the isoforms differ in tissue distribution and serum half-life. As a ~37 kDa glycoprotein rather than a small peptide, follistatin-344 has significant bioavailability challenges for subcutaneous or intramuscular injection, and no human pharmacokinetic data supports assumed tissue distribution from these routes. The clinically validated delivery route in humans has been AAV gene therapy, which is mechanistically distinct from injecting recombinant protein.
Dosing protocols
Dosing & administration
Dosing reflects protocols reported in research and community literature for educational purposes. It is not medical advice or a recommendation. Most peptides here are not approved for human use.
Reconstitution
Reconstitute with bacteriostatic water. A 1 mg vial + 1 mL BAC water = 1000 mcg/mL, so 5 units on a 100-unit insulin syringe = 50 mcg. Refrigerate the reconstituted vial (2-8C) and use within 28 days; store lyophilized product at -20C.
Beginner
- Dose
- 50 mcg
- Frequency
- Once daily
- Timing
- Consistent time each day
- Duration
- 4 weeks
- Route
- Subcutaneous
Entry-level cycle; assess strength and mass changes at the end of the cycle.
Intermediate
- Dose
- 75-100 mcg
- Frequency
- Once daily
- Timing
- Consistent time each day
- Duration
- 6 weeks
- Route
- Subcutaneous
Combine with progressive resistance training for synergy.
Advanced
- Dose
- 100 mcg
- Frequency
- Once daily (some protocols use BID during cutting phases)
- Timing
- Consistent daily timing
- Duration
- 6 weeks followed by a 4-week washout
- Route
- Subcutaneous or intramuscular
Twice-daily dosing appears in some advanced cutting-phase protocols; higher exposure amplifies off-target TGF-beta concerns.
- Community dosing ranges cluster at 50-100 mcg once daily, cycled 4-6 weeks with a 4-week washout; these figures come from community protocol docs, not from human clinical trials.
- There is no FDA-approved dosing framework and no validated human PK, so all injectable protocols are experimental and unverified.
- Product quality is a major variable: a 344-amino-acid glycoprotein is difficult to synthesize reliably at gray-market scale, and independent testing has found inconsistent or absent follistatin content in many vials. Verify which isoform (FS-288, FS-315, FS-344) is being sold and demand an independent HPLC/mass-spec certificate of analysis.
- Common research vial sizes are 1 mg, 2 mg, and 5 mg.
Evidence
Research & clinical studies (2)
The transgenic expression of human follistatin-344 increases skeletal muscle mass in pigs
Transgenic Duroc pigs with muscle-specific follistatin-344 overexpression showed significantly increased lean muscle mass and reduced body fat with myofiber hypertrophy, and no cardiac hypertrophy or reproductive abnormality.
PMID 27787698A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy
AAV1-delivered follistatin-344 injected into the quadriceps of six Becker MD patients improved 6-minute walk distance by 29-125 meters in four of six patients, with reduced fibrosis, increased fiber size, and no adverse effects.
PMID 25322757Combinations
Stacking & blends
GH-Driven Hypertrophy Stack
Combine growth-hormone-driven anabolism with myostatin antagonism for maximal hypertrophy
GH secretagogues raise endogenous GH/IGF-1 to boost protein synthesis while follistatin removes the myostatin brake, layering two independent anabolic mechanisms.
Muscle Growth + Connective Tissue Support
Support tendons and connective tissue during rapid muscle gain
BPC-157 promotes tendon and soft-tissue repair, offsetting the injury risk that can accompany rapid strength and mass increases from myostatin inhibition.
Safety
Side effects & considerations
Commonly reported effects
Contraindications & cautions
- Active malignancy or cancer
- Cardiovascular disease, cardiomyopathy, or left ventricular hypertrophy
- Pregnancy and breastfeeding
- Prostate conditions
- Active wound healing or post-surgical recovery (TGF-beta inhibition concerns)
Human safety data at performance doses is essentially absent. The mechanistic concern is broad TGF-beta family binding affecting cell proliferation across many tissues, which has not been characterized in humans; theoretical risks include cardiac muscle hypertrophy with prolonged use, off-target effects on wound healing and immune function, and reproductive effects via activin/gonadotropin regulation. Absence of reported acute events in unsystematic user populations is not evidence of long-term safety. Gray-market product misrepresentation is itself a significant risk factor. Professional oversight is strongly recommended; this is not suitable for self-administration.
FAQ
Follistatin 344 — common questions
What is Follistatin-344?
It is the 344-amino-acid tissue-bound isoform of the natural follistatin protein, an activin-binding glycoprotein that neutralizes myostatin (GDF-8) and related TGF-beta family members (activin A, GDF-11). By sequestering these negative regulators, it removes the brake on skeletal muscle growth and supports anabolic muscle remodeling.
Does Follistatin-344 actually build muscle in humans?
The myostatin pathway is real, and myostatin-null animals and humans develop dramatic hypertrophy. But there are zero human clinical trials of injectable follistatin-344 at performance doses, no pharmacokinetic data, and no safety characterization. The dramatic muscle growth in the literature comes from transgenic and viral gene-therapy models, not from injecting the protein.
Does it only target myostatin?
No. Follistatin binds activin A, activin B, and GDF-11 in addition to myostatin. These other targets regulate cell growth across many tissues, so calling it a selective myostatin antagonist mischaracterizes the biology and understates its off-target profile.
Is Follistatin-344 FDA-approved?
No. It has no FDA approval for any indication and is sold as a research-use-only compound. Follistatin gene therapy is in early clinical development for muscular dystrophy, but that is a separate delivery method with separate regulatory status. It is on the WADA Prohibited List as a myostatin function modifier.
Why is product quality such a concern?
Follistatin-344 is a 344-amino-acid glycoprotein with complex three-dimensional structure; reliable synthesis at small/gray-market scale is difficult. Independent testing frequently finds inconsistent, degraded, or absent follistatin content, so buyers may be receiving something other than functional follistatin. Standard peptide HPLC has limited discriminating power for a glycoprotein.
Does Follistatin-344 affect the heart?
Myostatin is expressed in cardiac tissue as well as skeletal muscle, so the inhibition mechanism raises theoretical concerns about cardiac effects with prolonged use. Clinical substantiation is limited, but the underlying biology supports caution.
How is it dosed in research contexts?
Community protocols cluster at 50-100 mcg subcutaneously once daily, cycled 4-6 weeks with a 4-week washout. These numbers are not from human clinical trials and there is no FDA-approved dosing framework.
