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Follistatin-344

Status: Preclinical / Research peptide, , not approved for human use
Evidence: Small human trials, mixture and gene therapy only, graded on 2 research benches

Reviewed 2 October 2026

01Overview

What Follistatin-344 is

Follistatin binds and neutralizes myostatin (GDF-8) - the primary negative regulator of skeletal muscle growth. Originally isolated from porcine ovarian fluid in the 1980s, the synthetic peptide form has become a research compound for studying myostatin antagonism and skeletal muscle hypertrophy.

Naturally occurring follistatin forms (the mature FS288 and FS315, made from the 317- and 344-residue precursors; UniProt P19883) differ in tissue distribution and serum half-life. The 344 variant is the most-studied for muscle research. Knockout mouse models lacking myostatin (or with high follistatin expression) show 2-3x normal muscle mass.

How it works

Follistatin binds and sequesters myostatin (GDF-8), preventing myostatin from activating the activin-receptor-mediated signaling pathway that normally suppresses muscle growth. Without myostatin signaling, satellite cells proliferate more aggressively, myoblast fusion is enhanced, and muscle protein synthesis exceeds catabolism. Follistatin also binds activin A and other TGF-beta family members, broadening its inhibition profile beyond myostatin alone. Note: the satellite-cell proliferation and muscle-protein-synthesis effects described above reflect follistatin's established molecular mechanism and its preclinical (cell-culture and animal) biology; they have not been demonstrated for the injectable Follistatin-344 research peptide in humans, for which no controlled efficacy or pharmacokinetic data exist.

Studied for

Muscle hypertrophy
Myostatin biology
Sarcopenia
Muscular dystrophy
TGF-beta family

Benefits listed

Myostatin antagonism for skeletal muscle growth
Satellite cell proliferation enhancement
Activin-A binding (broader TGF-beta family inhibition)
Research into muscular dystrophy and sarcopenia

02Research

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What the research shows

Graded on 2 research benches

Reference pages that put Follistatin-344 next to the compounds people pair it with: roles, evidence, overlap and conflicts. No dosing. Research use only.

Key research findings

Follistatin's inhibition of myostatin (GDF-8) and activin A is well characterized in preclinical cell-culture and animal models, where increasing follistatin reliably drives skeletal muscle growth. Direct human evidence, however, exists only for AAV-follistatin GENE THERAPY, not for an injected protein. In a proof-of-principle Phase 1/2a trial, the alternatively spliced follistatin isoform FS344 was delivered as an AAV1.CMV.FS344 vector by intramuscular quadriceps injection to Becker muscular dystrophy patients; several subjects improved on the 6-minute walk test with favorable muscle histology and no serious adverse events [PMID:25322757]. The same translational program describes initiating AAV-follistatin gene transfer to the quadriceps in Becker muscular dystrophy and sporadic inclusion body myositis [PMID:22609847]. Critically, these are gene-therapy studies in which muscle cells are engineered to produce follistatin internally. The injectable Follistatin-344 research peptide has no human efficacy trials and no published human pharmacokinetic data; any muscle-building expectations for subcutaneous FST-344 are extrapolated from gene-therapy and animal research, not demonstrated for the injected peptide itself.

Safety and side effects

Limited human safety data. Anecdotal AEs: injection site irritation, mild water retention, transient blood pressure changes. Theoretical concerns: cardiac muscle hypertrophy with prolonged use, off-target inhibition of other TGF-beta family members affecting wound healing or immune function.

On PubMed

924 PubMed results for the search follistatin[ti] NOT ("follistatin-like"[ti] OR "follistatin-related"[ti]), counted 2 October 2026. A search count, not a count of studies on Follistatin-344.

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Safety and side effects
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03Safety

Follistatin-344 side effects and interactions

Side effects

Common

Injection site irritation (anecdotal)
Mild water retention (anecdotal)
Transient soreness in trained muscles (anecdotal)

Serious events

Theoretical cardiac hypertrophy with prolonged use
Off-target TGF-beta inhibition affecting wound healing
Long-term human safety data unavailable

Who should not use it

Contraindications

Active malignancy. Pregnancy and breastfeeding. Cardiomyopathy or left ventricular hypertrophy. Active wound healing or post-surgical recovery (TGF-beta inhibition concerns). Prohibited in sport. The World Anti-Doping Agency 2026 Prohibited List, in force from 1 January 2026, lists myostatin-binding proteins including follistatin under section S4.3, agents preventing activin receptor IIB activation.

Interactions

Not in our record

Our record lists no interactions for Follistatin-344. That means none are recorded here, not that none exist.

This interaction data is compiled from published research and community reports. It may not be exhaustive. Always consult a healthcare professional before combining compounds.

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04Dosing

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Follistatin-344 dosage and protocols

Dose range: 50-100 mcg
Dosing: Once daily
Common vials: 1mg, 2mg, 5mg

Dosing summary

Dose: 50-100 mcg
Route: Subcutaneous
Frequency: Once daily
Duration: 4-6 weeks

Protocols

Beginner protocol

50 mcg subcutaneous once daily for 4 weeks. Assess strength/mass changes at end of cycle.

Intermediate protocol

75-100 mcg subcutaneous once daily for 6 weeks. Combine with progressive resistance training for synergy.

Advanced protocol

100 mcg subcutaneous once daily for 6 weeks, with 4-week washout. Some advanced protocols use BID dosing during cutting phases.

Common vial sizes

Reconstitution and handling notes

Reconstitute with bacteriostatic water. Refrigerate reconstituted vial. Use within 28 days.

Stacking notes

Stacks with CJC-1295 + Ipamorelin for GH-driven hypertrophy + myostatin antagonism. Pair with BPC-157 for tendon support during rapid muscle gain. Avoid stacking with Activin-receptor antagonists (additive effects on TGF-beta family).

Additional dosage notes

Reconstitute with bacteriostatic water. A 1mg vial + 1mL BAC water = 1000 mcg/mL. 5 units = 50 mcg on a 100-unit insulin syringe.

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05Prices

Follistatin-344 prices

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06Chemistry

Chemistry and structure

Molecular formula: Glycoprotein (~37 kDa)
Molecular mass: ~38 kDa glycosylated (mature FST-315 glycoprotein); ~35 kDa for the unglycosylated ~315-residue core. A large glycoprotein, not a small peptide.
Amino acid sequence: Follistatin-344 is a 344-residue precursor protein (29-residue signal peptide + 315-residue mature chain; isoform FST-315, human UniProt P19883), not a short synthetic peptide. The mature glycoprotein comprises an N-terminal domain plus three follistatin domains and is N-glycosylated, so a simple linear peptide sequence is not the relevant descriptor.
Half-life: Short; native follistatin protein is cleared rapidly (minutes to a few hours in vivo). No formal pharmacokinetic data exist for injected Follistatin-344 (FST-344).

08Questions

Frequently asked questions

What is Follistatin-344 used for in research?

Follistatin-344 is named for the 344-amino-acid precursor of follistatin [PMID:3380788]; once its 29-residue signal peptide is removed, the mature glycoprotein (FST-315) is 315 residues long (UniProt P19883). Follistatin binds and neutralizes myostatin (GDF-8) - the primary negative regulator of skeletal muscle growth. Originally isolated from porcine ovarian fluid in the 1980s, the synthetic peptide form has become a research compound for studying myostatin antagonism and skeletal muscle hypertrophy.

What forms does Follistatin-344 come in?

Follistatin-344 is available in vials, capsules, and sprays forms.

How much does Follistatin-344 cost?

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