Follistatin-344

Last Updated: August 2026

Follistatin-344 (FS-344) is a specific isoform of follistatin — a single-chain glycoprotein encoded by the FST gene that binds and neutralizes members of the TGF-β superfamily, most notably myostatin and activin A. It is a more specific entry alongside the general Follistatin profile: FS-344 is the 344-amino-acid precursor form used in most injectable and gene-therapy research, processed in the body toward the freely circulating FS-315 isoform. It is not approved and is supplied for research use only.

What is Follistatin-344 and how does it differ from other follistatin isoforms?

The FST gene produces several splice variants — FS-288 (tissue-bound, gonad-concentrated), FS-315 (circulating, muscle-targeting), and the FS-344 precursor that is processed toward FS-315 — and FS-344 is favored in research because it generates the bioactive circulating form once introduced into a biological system. Its 27-residue C-terminal extension affects tissue retention relative to the shorter FS-315.

How does Follistatin-344 build muscle?

By binding myostatin (and activin A) with high (picomolar) affinity, FS-344 prevents them from activating ActRIIB and the downstream SMAD2/3 cascade that normally suppresses muscle protein synthesis — releasing the brake and permitting hypertrophy and satellite-cell-driven growth. Because it also suppresses activin, it can affect pituitary FSH signaling — a reproductive-endocrine consideration.

What does the research on Follistatin-344 show?

The strongest human evidence is a gene-therapy trials using the follistatin FS344 construct (rAAV1.CMV.FS344, "AAV1-FS344") in Becker muscular dystrophy and sporadic inclusion body myositis reported increased muscle volume and functional improvements over ~2 years without serious adverse events1 source; preclinical data in mice, primates, and dogs consistently show large (2–3×) muscle-mass increases. Human data for injectable follistatin peptide (as opposed to the gene therapy) is minimal. Evidence level: Gene-therapy human trial + strong preclinical; injectable-peptide human data minimal.

What are the safety concerns and regulatory status?

Follistatin-344 is not approved, its long-term human safety as an injectable is not established, and it is prohibited in sport at all times — the WADA Prohibited List names follistatin under S4.3 (Agents Preventing Activin Receptor IIB Activation), as a "myostatin-binding protein"; Follistatin-344 is a follistatin isoform and is covered by that entry (as of August 2026)1 source; activin suppression also carries reproductive-endocrine implications. See the legal status guide.

Why does vendor verification matter, and how does Peptigrity verify?

Follistatin is an expensive recombinant protein, so implausibly cheap "follistatin-344" is a red flag, and counterfeits (including His-tagged constructs) are common — HPLC purity and mass-spec identity are the objective checks. Peptigrity collects independent third-party Certificates of Analysis for follistatin-344 from shops' official channels and verifies each for authenticity before publishing. Because shops choose which COAs to publish, results reflect the batches shops have made public rather than every production batch — a selection bias we state openly. A community-funded Testing Grant to purchase and test vials anonymously is in development. Follistatin's glycoprotein/recombinant nature means HPLC purity and mass-spec identity (and ideally checks for His-tagged constructs) matter more here than for small peptides. Tests in the database come from independent labs such as Janoshik Analytical, Freedom Diagnostics, and Chromate; the trust score weights independent lab purity and community reviews equally (50/50). See the COA red-flags guide.

Educational information only; not medical advice. Follistatin-344 is not approved for human use. Consult a qualified healthcare provider. Peptigrity does not sell, endorse, or recommend products or vendors.