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Growth & GHPeptideEvidence C4 cited

Follistatin 344

Myostatin Inhibitor Peptide

aka FS-344 · FST · follistatin · activin binding protein

A glycoprotein that binds and neutralises myostatin, the protein that naturally limits muscle growth.

Molecular wt
38007g/mol
Half-life
6 h
estimated
Tmax
4 h
Route
Subcutaneous injection

Sequence

One-letter344 residues

MVRARHQPGGLCLLLLLLCQFMEDRSAQAGNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEW

Read this before quoting the sequence
NOT a research peptide - this is a protein isoform, and should not be presented in a peptide-vial template. 'Follistatin 344' (FST344) denotes the 344-amino-acid PRECURSOR encoded by the longer human FST transcript. UniProt P19883 (FST_HUMAN) canonical isoform 1 is 344 residues; residues 1-29 are the signal peptide and residues 30-344 are the mature secreted chain of 315 residues, which UniProt names isoform 'FS315' / 'FS-315'. The alternative isoform 2 is a 317-residue precursor yielding the 288-residue mature form 'FS288'. So FST344 is the gene/transcript-level name; the circulating protein it produces is FS-315. Follistatin is a glycoprotein and an activin/myostatin/GDF11-binding antagonist, not a synthetic peptide. The sequence above is the full 344-residue precursor including the signal peptide.
Source ↗

Mechanism of action

Follistatin 344 works by binding to and inhibiting myostatin, a protein that limits muscle growth. This inhibition allows for increased muscle cell proliferation and differentiation. Additionally, follistatin can bind to other members of the TGF-beta superfamily, potentially influencing various cellular processes. The result is enhanced muscle growth and regeneration.

What the evidence actually shows

Grade C

There are currently no robust human clinical trials specifically investigating Follistatin 344. Most evidence comes from animal studies and in vitro experiments, which suggest potential for muscle growth. Human data is limited and primarily anecdotal, highlighting a significant gap in clinical research.

Regulatory status

Status
No follistatin product is approved anywhere. There is no approved recombinant follistatin protein and no approved follistatin gene therapy. Development has been in academic AAV gene-therapy trials only.
Clinical stage
Phase 1/2a gene-therapy trials (AAV1-FS344) in Becker muscular dystrophy and sporadic inclusion body myositis; no later-stage programme identified.
WADA
Prohibited at all times. WADA 2026 Prohibited List section S4.3 (Myostatin inhibitors) names 'Myostatin-binding proteins (e.g. follistatin, myostatin propeptide)'. This is S4, NOT S2.
UK
research_compound

In the UK, Follistatin 344 is considered a research compound and is not approved for medical use. It is primarily used in laboratory settings.

Source ↗

Pharmacokinetics

Half-life
6 h
Tmax
4 h
Absorption
subcutaneous
Elimination
renal
Washout
5 days
Low-confidence pharmacokinetics
These figures are recorded as estimated rather than measured in a published PK study. Treat them as an order of magnitude. Anything downstream of them — accumulation, steady state, washout — inherits that uncertainty.

Dosing — what backs each figure

The only human follistatin-344 studies are gene therapy, not peptide injection: AAV1.CMV.FS344 delivered once by direct bilateral intramuscular quadriceps injection at 3 x 10^11 vg/kg/leg (cohort 1) or 6 x 10^11 vg/kg/leg (cohort 2) in Becker muscular dystrophy (PMID 25322757), and 6 x 10^11 vg/kg in sporadic inclusion body myositis (PMID 28279643), plus a 43-participant phase 1 FST344 plasmid study by Minicircle (NCT06411366) that publishes no dose. There is no established - or even published - human dose for injected follistatin-344 protein.

PreclinicalAnimal studies — not a human dose

  • AAV-delivered follistatin (FS344) to muscle increased muscle size and strength; translational dose-ranging preceding the human trials

    mouse and non-human primate (macaque) · intramuscular AAV gene transfer · PMID 19208403

Animal doses do not convert to human doses by body weight alone. Route matters too — a compound dosed intraperitoneally in mice tells you little about subcutaneous use.

Commonly circulatedNot established by any study
Dose
100-300 mcg/day
Frequency
Daily for 10-30 days
Cycle
10-30 day cycles· unsourced

Why this isn't evidence
No human (or animal) study has ever injected follistatin-344 protein at a microgram-per-day dose: every human trial delivered the FS344 GENE - AAV1.CMV.FS344 at 3-6 x 10^11 vg/kg/leg as a one-off intramuscular gene transfer - which is a completely different modality that cannot be converted into a daily microgram peptide dose.

This figure is shown because it is what circulates and what people search for — not because it is supported. Cycle lengths in particular tend to be convention copied between compounds rather than anything derived from a compound's own pharmacokinetics.

No established human dose
No approved label or completed human trial establishes a dosing regimen for this compound. Anything presented as a standard protocol for it — anywhere — is someone's convention rather than a finding.

Handling and storage

No compound-specific stability data exists
No approved follistatin product exists, so no regulatory storage specification exists. No published stability study for a follistatin 344 preparation could be retrieved. Note also that Reichel 2019 found that only 9 of 17 tested black-market 'follistatin 344' products actually contained follistatin, so vendor storage claims describe products of unverified content. General peptide handling still applies — reconstitute gently, keep it cold, keep it dark — but any specific figure you see quoted for this compound elsewhere is someone's assumption, not a measurement.
→ Reconstitution walkthrough→ Reconstitution calculator

Safety

Commonly reported
  • ·Injection site reactions
  • ·Muscle pain
Rarely reported
  • ·Potential for abnormal muscle growth
  • ·Unknown long-term effects
Contraindications
  • ·Pregnancy
  • ·Breastfeeding
  • ·"Known hypersensitivity to follistatin"
Drug interactions
  • ·None well-documented due to limited human research

Reported combinations

Reported as synergistic
  • ·Creatine
  • ·"Branched-chain amino acids (BCAAs)"
Reported as antagonistic
  • ·Myostatin inhibitors (may lead to excessive muscle growth)

Combination claims in this dataset are largely unsourced and should be treated as folk knowledge until a citation appears beside them.

References (4)

Data provenance

Chemistry and citations on this page were checked against primary sources on 2026-08-14. Values that could not be verified were left blank rather than filled with a plausible guess.

Could not verify
molecularFormula, casNumber, pubchemCid, storage, reconstitution

Research use only
This profile is educational reference material. It is not medical advice, not a prescription, and not an endorsement of self-administration. Compounds discussed here are research chemicals and most are not approved for human therapeutic use.

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