Follistatin-344

Areas of active research — not promised effects

Each tag links to other compounds with research into that goal. Research use only: these are areas of study, not human-use claims.

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FST-344 has no FDA approval for any human therapeutic indication. As a recombinant protein of 344 amino acids (~38 kDa), it is regulated as a biologic under the Public Health Service Act and cannot be compounded by 503A pharmacies, which lack a biologics license. The April 2026 FDA/HHS Category-2 reclassification (docket FDA-2025-N-6895, effective April 23, 2026) removed certain small unapproved peptides from the Category 2 prohibition list and scheduled PCAC review for July 23–24, 2026; FST-344 was not identified as one of the approximately 12 peptides addressed by that action, and its status as a large protein places it outside the scope of the 503A compoundable-peptide framework regardless. Sale, supply, or human administration outside an FDA-authorized IND is not permitted.

Confirmed high-severity market-integrity event (enforcement / recall / counterfeit)

Transparent blend · bci-1.0 · never paid-placement

Primary name

Follistatin-344

Length

344 aa

Origin

Naturally occurring splice isoform of human follistatin (gene FST, UniProt P19883). FST-344 differs from the shorter FST-288 isoform by a 27-residue C-terminal extension that reduces heparin-binding affinity and promotes systemic circulation rather than local extracellular-matrix retention. The recombinant form produced for research use is expressed in mammalian or insect cell systems and recovered as a lyophilized protein; it is not a synthetic peptide.

Appearance

White to off-white lyophilized powder (vendor-typical for recombinant glycoproteins)

Solubility

Soluble in aqueous buffers; typically reconstituted in sterile phosphate-buffere…

Sequence · one-letter

Stability: Sensitive to elevated temperatures and repeated freeze-thaw; glycoprotein susceptibility to aggregation and deamidation. Stability data specific to RUO FST-344

Vial sizes

1 mg

Purity grades

≥95% SDS-PAGE / ≥95% HPLC

Salt forms

Free base (primary)

• GHS hazard class on file
• PPE & spill response
• Disposal guidance
• Not-for-human-consumption posture

How much research exists, and of what maturity — never a verdict on whether it works.

Mechanism of action

• Follistatin-344 binds myostatin (GDF-8), activin A, activin B, and selected bone morphogenetic proteins with picomolar-to-nanomolar affinity by wrapping around the ligand surface and sterically occluding the ActRIIB receptor-binding epitope
• Sequestration of these ligands prevents downstream phosphorylation of SMAD2 and SMAD3, attenuating their transcriptional repression of muscle protein synthesis and satellite-cell differentiation programs
• The dual inhibition of both myostatin and activin A produces greater hypertrophic responses in rodent models than myostatin blockade alone, because activin A independently maintains a separate inhibitory tone on muscle mass via the same receptor
• In transgenic mouse experiments, follistatin overexpression has produced muscle-mass increases of two-to-three-fold relative to wild-type controls, exceeding the gains seen with myostatin knockout, underscoring the contribution of other follistatin ligands to the net anabolic effect (reviewed in PMID 41966639)

Pharmacokinetics (ADME)

Half-life

Circulating half-life estimated at approximately 24–28 hours in rodent models for FST-344; substantially longer than FST-288 (~2–4 hours) due to reduced heparin-binding and matrix sequestration. No formal pharmacokinetic study of recombinant FST-344 protein in humans has been published.

Clearance

Systemic clearance thought to occur primarily via receptor-mediated endocytosis and renal filtration; specific clearance values not published for FST-344 in peer-reviewed literature.

PK–PD note: The extended circulating half-life of FST-344 relative to FST-288 was the rationale for selecting the FST-344 isoform for the AAV1-FS344 gene therapy vector used in neuromuscular disease trials (NCT06…

Reading the evidence

• Evidence quality and gaps vary by application — see the cited grades above.
• Indexed-article counts span all evidence tiers, not only completed human trials.
• No first-party human-dosing, efficacy, or benefit claims are made here.

Key reviews & evidence-gap sources

• Rodino-Klapac LR, Haidet AM, Kota J, Handy C, Kaspar BK, Mendell JR. Inhibition of myostatin with emphasis on follistatin as a therapy for muscle disease. Muscle Nerve. 2009;39(3):283-296. — Anchoring narrative review; preclinical AAV1-FS344 data mice-to-monkeys; basis for clinical gene therapy program.
• Al-Zaidy SA, Sahenk Z, Rodino-Klapac LR, Kaspar B, Mendell JR. Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy. J Neuromuscul Dis. 2015;2(3):185-192. — Reports first-in-human FS344 gene transfer trial results (BMD cohort).
• Mendell JR et al. A Phase 1/2a Follistatin Gene Therapy Trial for Becker Muscular Dystrophy. Mol Ther. 2015. — Phase 1/2a BMD trial publication; six BMD patients, intramuscular AAV1.CMV.FS344.

1 registered trial — 0 currently recruiting.

Phase 1
NCT06411366
Phase I: Safety and Efficacy of an Injectable Follistatin Plasmid Gene Therapy in Humans

COMPLETED

Summary (literature)

The principal human safety signal for injectable recombinant FST-344 is central serous chorioretinopathy (CSCR), documented in a retrospective case series of bodybuilders using high doses (PMID 32671599); the mechanism is hypothesized to involve disruption of activin/follistatin …

WADA status

Prohibited in-competition and out-of-competition under the WADA 2026 Prohibited List. FST-344 falls under Section S2 (Peptide Hormones, Growth Factors, Related …

Dominant research route: Intramuscular (AAV1.CMV.FS344 gene transfer) for human studies; subcutaneous (nanoparticle mRNA) for animal PK/mechanism studies.

Human gene therapy (AAV1.CMV.FS344) delivered by direct bilateral intramuscular quadriceps injection in Becker muscular dystrophy (BMD) and sporadic inclusion body myositis (sIBM) patients; Phase 1, single-group, non-randomized, n=15 enrolled, completed Oct 2017. Dose cohorts 2E11, 3E11, and 6E11 vg/kg per quadriceps.

Bioavailability: Local intramuscular depot of AAV vector transduces muscle to express follistatin-344 transcript (confirmed by RT-PCR); not a systemically absorbed peptide. Primary outcome was safety; secondary outcomes included 6-minute walk test, MRI, and muscle biopsy fiber size.

This is the dominant HUMAN route studied for follistatin-344, but as AAV-mediated gene transfer rather than exogenous recombinant protein injection. The FS344 isoform was selected over FS288 to reduce off-target binding.

Mouse model: subcutaneous administration of follistatin mRNA-loaded polymeric nanoparticles; follistatin serum levels elevated for 72 h post-injection; ~10% increase in lean mass after 8 weeks of repeated injections vs controls.

Bioavailability: Nanoparticle-encapsulated mRNA entered systemic circulation following SC injection, accumulated/internalized in liver where mRNA was translated to follistatin. Study measured follistatin serum kinetics, not free-peptide SC bioavailability.

Animal (mouse) in-vivo study of nanoparticle-delivered follistatin mRNA, not free follistatin-344 protein. Demonstrates SC route can achieve systemic follistatin expression via hepatic translation.

Referenced as comparator for SC bioavailability estimation in rodent models (community-aggregated secondary source); no primary IV PK study retrieved.

Bioavailability: Community aggregator cites ~40–60% SC bioavailability relative to IV dosing in rodent models, attributed to lymphatic clearance and proteolytic degradation at injection site. Primary IV pharmacokinetic source not located.

Layer B (de-identified aggregate community). IV appears only as a PK reference comparator in secondary aggregator content; no primary peer-reviewed IV follistatin-344 PK study was retrieved.

Reported as a common route in mouse-model follistatin research with rapid peritoneal absorption (aggregator secondary source); no primary IP study retrieved.

Bioavailability: No primary PK values located; aggregator describes rapid peritoneal absorption in mouse models.

Layer B (de-identified aggregate community). IP route mentioned only in secondary aggregator overview; no primary peer-reviewed IP follistatin-344 study was retrieved to confirm.

Animal & human figures are kept visibly separate so studied animal doses are never misread as human guidance.

Sorted A–Z by vendor — never by price

Weekly median $/mg from the live vendor crawl.

Researched storefront prices, bucketed

p25 $103.22 · median $138.00 · p75 $157.48 · 6 researched vendors

Legit, COA-backed band: $99.00–$162.00/mg.

Value rule: don't just buy the cheapest — a price under $3/mg is a red flag. Pair price with COA and independent-test grade.

Estimated cost of research (10 mg)

Vial (best researched price)

$990

Bacteriostatic water (generic estimate)

$6

Syringes / supplies (generic estimate)

$12

What each test proves — general guidance, plus this compound's researched purity data

Purity on the current market (researched)

Vendor and third-party lab reports span ~95% to >99.8% HPLC purity (e.g., Medica Depot ≥95%; Pure Bio Labs/Amino USA >99%; 24Peptides/Grail Formula >99.8% via Liquilabs; QSC ≥99% with Janoshik COA).

Independent labs cited for this compound

No FDA recalls, market withdrawals, or seizure actions naming follistatin-344 were found in FDA enforcement databases; the compound has no FDA-approved drug product to recall.

Buyer red-flag checklist

• No FDA-approved follistatin drug product exists; all 'follistatin-344' sold as research-chemical/lyophilized powder is unapproved for human use.
• Black-market availability documented in peer-reviewed anti-doping literature (Reichel et al., 2019).
• WADA-prohibited under S4 (and gene-doping M3 for follistatin-increasing methods); athletes face sanctions.
• Black-market FS344 products are recombinant/His-tagged, distinguishable from endogenous follistatin — indicating non-pharmaceutical manufacturing origin.
• Vendor purity claims vary widely (95% to >99.8%) with no uniform pharmacopeial standard; lot-specific COAs are the only verification.
• FDA Import Alert 66-71 (DWPE of unapproved HGH) does not name follistatin; no compound-specific FDA import alert was found, so enforcement against follistatin imports relies on general unapproved-new-drug provisions rather than a dedicated red-list.

GMP vs research-grade: the chemistry (SPPS + HPLC + MS) is identical — the difference is the quality system.

Underdosing / mislabeling: No published aggregate underdosing prevalence from independent labs (Janoshik/MZ Biolabs/Finnrick) specific to follistatin-344 was located; only a single Janoshik test record (test 96852) for an FST344 vendor lot was identified, which is insufficient to compute a prevalence figure.

• An RUO label is not an import exemption — CBP judges actual intended use.
• Lyophilized powder is ambient-stable in transit; temperature control needed for > 7-day transit.
• US-warehouse vendors dodge import scrutiny — they cost more but ship more reliably.

Every item dated & sourced

Prohibited at all times (in- and out-of-competition) under S4.3 "Agents preventing activin receptor IIB activation" — specifically enumerated as a myostatin-binding protein (e.g. follistatin, myostatin propeptide). First specifically enumerated on the 2019 WADA Prohibited List; continues on the 2026 Prohibited List.

No granted patents identified in current seed. Composition-of-matter coverage is limited given the peptide's synthetic origin.

• IACUC / IRB research context
• RUO buyer responsibilities & documentation
• Veterinary / alternative-use where lawful
• Jurisdiction-aware "who may lawfully obtain"

What people discuss

Reported concerns — discussion, not established effects

Reading caveats

• Small self-reported anecdotal sample skewed to bodybuilding communities
• Frequent conflation of gene-therapy trial results with injectable-peptide effects
• Vendor-affiliated promotional content present in aggregator guides
• Survivorship bias: negative-experience posters more likely to post than silent non-responders

Manually researched from reddit, youtube, x— theme weights are research estimates, not live counts; aggregated & de-identified. No individual posts, quotes, or usernames are ever shown.

Relative research / market volume — populated once the activity stream is wired

Inline tooltips for lyophilized, RUO, EU/mg, SPPS, 503A and more.

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• How to read a COA
• Free base vs acetate
• Understanding evidence grades

344-amino-acid glycoprotein isoform of human follistatin that neutralizes myostatin and activins to relieve inhibitory control over skeletal muscle growth. Approximately 5 articles are indexed (literature last scanned 2026-05-29). US regulatory status: Unapproved biologic; research use only. Research use only.

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