Thymosin beta-4 monograph

Thymosin beta-4

Overview

Thymosin beta-4 is a 43-amino-acid endogenous peptide/protein best known for binding G-actin and influencing cell migration, inflammation, and tissue repair. Human use as an ergogenic or performance drug is not established; most useful data come from preclinical and limited ophthalmic clinical development rather than bodybuilding studies. For coaching purposes, TB-4 should be treated as an investigational peptide with uncertain benefit, unclear pharmacokinetics in humans, and meaningful contamination/quality and antidoping risk.

Pharmacokinetics & Mechanism

• Class: Endogenous peptide; actin-binding/regulatory peptide
• Mechanism of action: TB-4 is an actin-sequestering peptide that binds monomeric G-actin and inhibits G-actin polymerization into F-actin, which can alter cytoskeletal dynamics, cell motility, migration, and wound-healing responses. Reviews also describe anti-inflammatory, anti-oxidative, anti-apoptotic, antifibrotic, and pro-angiogenic effects, with downstream signaling linked to the SRF-MRTF-G-actin transcriptional pathway. Human target engagement is not well established for performance use.
• Target(s): Primary biochemical target: G-actin/actin monomer sequestration. Downstream pathways described in the literature include SRF-MRTF-G-actin signaling, inflammatory mediator signaling, oxidative stress pathways, apoptosis-related signaling, and pro-angiogenic/fibrotic remodeling pathways. No validated human receptor target is established.
• Route(s) of administration: Research and preclinical literature includes systemic/intravenous administration, local/topical ocular use, injectable/local delivery in experimental models, and transdermal formulation research. Community use commonly describes subcutaneous or intramuscular injection, but that is anecdotal and not clinically established.
• Onset: Not well established in humans. Preclinical biologic effects may occur soon after administration in experimental models, but no reliable human onset window is established for performance or recovery use.
• Half-life: Human half-life is not well established. In the available literature, TB-4 is discussed as a small endogenous peptide with ongoing pharmacology work, but robust human PK data are lacking. A related claim that an extended/DAC-like variant meaningfully changes half-life is not established in high-quality human data for TB-4 itself; treat any vendor/community half-life claims as speculative.
• Metabolism / clearance: Not well established in humans. As a peptide, TB-4 is expected to undergo proteolytic degradation and peptide clearance; one mouse biodistribution study examined serum, urine, and major organs, but human metabolic clearance pathways and elimination half-life are not established in the sources reviewed.