Every cell that migrates, divides or changes shape rebuilds its internal scaffolding to do it. Thymosin β4 is one of the molecules that manages that scaffolding, and TB-500 is its synthetic form.
TB-500 · Actin-binding peptide (thymosin β4)
Cells are not rigid. To close a wound, grow a new blood vessel or move through tissue, a cell constantly assembles and dismantles filaments of a protein called actin. Thymosin β4 holds actin building blocks in reserve and releases them where they are needed. Researchers study it because that control sits underneath many tissue processes. Most of the evidence is from cells and animals, with a small number of human trials in specific settings.
TB-500 is the synthetic form of thymosin β4 (Tβ4), a naturally occurring 43-amino-acid protein and the most abundant member of the β-thymosin family in human cells. The 5 mg batch tested independently for Pulse in December 2025 was identified as full-length thymosin β4 by mass spectrometry against an authentic standard; other presentations and batches have no published document. That identity matters because some products sold as “TB-500” are short fragments of the sequence, and the published evidence concerns the full-length protein.
Its best-established job is actin sequestration. Actin exists as single units (G-actin) that polymerise into filaments (F-actin) — the cytoskeleton, the cell’s internal framework. Tβ4 binds single actin units one-to-one and keeps a pool of them unpolymerised, which is how a cell controls when and where filaments form. The structure of that complex was resolved by X-ray crystallography in 2004 (Irobi et al.), making this one of the more firmly characterised mechanisms in this category.
The tissue-repair line of research follows from that mechanism. In mice, topical and injected thymosin β4 accelerated closure of full-thickness skin wounds and increased the migration of keratinocytes, the cells that resurface a wound (Malinda et al., 1999). In a mouse model of heart attack, Tβ4 activated a survival signalling enzyme (integrin-linked kinase) in heart muscle cells and reduced the area of damaged tissue (Bock-Marquette et al., 2004). A review by the group that first isolated the protein summarises the wider cell and animal work on migration, blood-vessel formation and inflammation (Goldstein, Hannappel and Kleinman, 2005).
Human evidence is topical and in specific settings. A randomised, double-blind, placebo-controlled phase 2 study at eight European sites applied thymosin β4 to venous leg ulcers in 73 patients, reported a safety profile comparable to placebo, and suggested faster healing at one concentration, with complete healing within three months in about a quarter of patients (Guarnera et al., 2010). A phase 2 randomised trial of thymosin β4 eye drops reported improvement in signs and symptoms of severe dry eye (Sosne et al., 2015). Both are topical formulations in defined patient groups; neither is evidence about injected material or musculoskeletal recovery.
The human wound studies are small phase 2 trials of topical preparations, the cardiac findings remain animal-only, and no controlled human trial of injected thymosin β4 for tissue or musculoskeletal recovery was identified, so whether those responses occur in people is unknown. Route, dose and formulation differ substantially between the published studies, and results from a topical eye preparation do not transfer to systemic use. Thymosin β4 is also present in almost every cell type, so the effects of adding more of it are not necessarily the same as the effects of the protein a cell already makes. Anti-doping status is a separate consideration: thymosin β4 and its derivatives are prohibited at all times under category S2 of the WADA Prohibited List.
TB-500 / thymosin β4 is not an approved medicine in Australia. It is prohibited at all times in sport under category S2 of the 2026 WADA Prohibited List.
Sources and status checked 2026-09-23
TB-500 — sizes and pricing