Follistatin-344 monograph

Follistatin-344

Overview

Follistatin-344 is the full-length human follistatin isoform commonly discussed in bodybuilding circles as a myostatin/activin-pathway antagonist. In physiology, follistatin binds and neutralizes members of the TGF-beta superfamily, especially activin and myostatin, which are relevant to muscle growth signaling. It is not an approved drug, and human dosing, pharmacokinetics, and performance outcomes are not well established.

Pharmacokinetics & Mechanism

• Class: Endogenous glycoprotein; follistatin isoform / recombinant peptide-protein research biologic
• Mechanism of action: Follistatin is a single-chain glycosylated protein that binds and neutralizes TGF-beta superfamily ligands, especially activin and myostatin, reducing downstream signaling through these pathways. By antagonizing myostatin/activin signaling, it can theoretically remove inhibitory brakes on skeletal muscle growth and differentiation. Any bodybuilding claims are extrapolated from biology, animal work, and limited human data; true performance effects of exogenous Follistatin-344 in humans are not well established.
• Target(s): Primary biologic targets: activins, myostatin (GDF-8), and other selected TGF-beta superfamily ligands. Downstream pathway: activin receptor type IIB / TGF-beta-SMAD signaling axis. Relevant receptor/pathway context includes myostatin signaling through TGF-beta receptors and SMAD family transcription factors.
• Route(s) of administration: Not well established in humans. Community/research use is usually described as subcutaneous or intramuscular injection of reconstituted peptide/protein solution; no approved route or labeled administration exists.
• Onset: Not well established in humans. Biological effects, if any, would likely not be immediate; no reliable human onset data for Follistatin-344 were found.
• Half-life: Not well established in humans. Half-life for Follistatin-344 specifically is not established; I did not find a reliable human PK source. Do not assume the short peptide-style half-life seen with some peptides. Any claims of a precise hours-long half-life are speculative. If someone is referring to folistatin gene therapy or other constructs, PK may differ substantially.
• Metabolism / clearance: Not well established. As an endogenous protein, follistatin would be expected to undergo proteolytic degradation and normal protein clearance pathways, but specific human metabolism/clearance data for exogenous Follistatin-344 are lacking.