Follistatin 344
Follistatin 344
Follistatin 344 is a 344-amino acid isoform of follistatin, an endogenous glycoprotein that acts as a potent antagonist of myostatin and other TGF-beta superfamily members. It is primarily used in research and performance contexts for its ability to promote skeletal muscle hypertrophy, reduce body fat, and enhance recovery by suppressing myostatin-mediated muscle growth inhibition. Interest in this peptide has grown significantly among athletes and bodybuilders seeking dramatic lean mass gains beyond what traditional anabolics provide.
Mechanism of Action
Follistatin 344 binds with high affinity to myostatin (GDF-8) and activin A, neutralizing their inhibitory signaling through the ActRIIB receptor and preventing downstream SMAD2/3 phosphorylation that would otherwise suppress muscle protein synthesis and satellite cell activation. By removing this biological 'brake' on muscle growth, Follistatin 344 allows for enhanced mTOR signaling, increased satellite cell proliferation, and augmented myofibrillar protein accretion. It also binds FSH-suppressing activins, which can produce secondary hormonal effects on reproductive and bone metabolism pathways.
Evidence by Health Goal(10 goals)
Dosing Protocols
Administered subcutaneously or intramuscularly, commonly into the target muscle belly (site-specific injection reported anecdotally)
Cycle: 10 days on, minimum 6-8 weeks off before repeating
Reconstitute lyophilized powder with bacteriostatic water. The 10-day cycle is the most reported protocol due to the peptide's long half-life and receptor downregulation concerns. Site-specific injections (into muscle bellies) are anecdotally used for localized hypertrophy but carry higher infection risk. Higher doses up to 200mcg/day have been reported but increase adverse effect risk substantially.
Safety & Side Effects
Follistatin 344 has a very limited human clinical safety database; most data come from animal models and anecdotal reports, making its risk profile poorly characterized in humans. It is not approved for human therapeutic use by the FDA or EMA, is classified as a research chemical, and poses serious theoretical risks including promotion of occult tumor growth and irreversible hormonal disruption — use in humans is considered experimental and carries meaningful unknown long-term risk.
Possible Side Effects
- !Injection site pain, swelling, and erythema
- !Tendon and connective tissue strain due to rapid muscle growth outpacing tendon adaptation
- !Suppression of FSH and potential disruption of reproductive hormone signaling
- !Abnormal or accelerated tissue growth including potential growth of pre-existing tumors
- !Acromegalic-like joint discomfort if used alongside GH/IGF-1
- !Gastrointestinal disturbances including nausea and cramping
- !Potential cardiovascular enlargement risk with prolonged or repeated use
- !Immune-mediated reactions or antibody formation against exogenous follistatin
Interactions
- -Additive myostatin suppression when combined with ActRIIB antagonists (e.g., YK11, RAD140) — may amplify muscle hypertrophy but also compound connective tissue strain risk
- -May potentiate anabolic effects of exogenous IGF-1 or GH, increasing risk of acromegalic side effects and organomegaly
- -Suppression of activin A may interfere with exogenous FSH-based fertility treatments — caution in individuals undergoing reproductive therapy
- -Concurrent use with anabolic-androgenic steroids may accelerate musculoskeletal imbalance, elevating tendon rupture risk
- -May theoretically reduce the suppressive signaling used by some cancer therapies that leverage TGF-beta pathways — contraindicated with active malignancy or cancer history
Cost & Where to Buy
A 1mg vial of research-grade Follistatin 344 typically costs $80–$180 from peptide vendors; a standard 10-day cycle at 100mcg/day uses 1mg total. Monthly cost depends on cycle frequency, vendor quality, and whether ancillaries (bacteriostatic water, syringes) are included. Purity and authenticity vary widely between vendors — third-party tested sources command higher prices.
Search on Amazon