TB-500 is the actin-binding heptapeptide fragment of thymosin beta-4 studied for tissue repair.

What TB-500 is, in one screen

TB-500 is a synthetic, N-acetylated heptapeptide with the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln — a single seven-residue fragment, not a blend. Those seven residues (17 through 23) are the actin-binding core of thymosin beta-4, a 43-amino-acid protein present in nearly every human cell and released by platelets and macrophages at sites of injury ^[1]. The fragment carries the part of the parent protein that grips actin; it does not carry the rest of it.

That distinction governs everything on this site. "TB-500" in commerce and in anti-doping science means the ~889 Da heptapeptide. Most of the published efficacy research, however, was run with full-length thymosin beta-4 (~4963 Da), not the seven-mer ^[5]. Where a finding used the full protein, this digest says so on the finding. It is not established that the isolated fragment reproduces the parent protein's downstream effects at the doses circulated in peptide research.

The headline numbers are honest ones. The fragment has zero completed controlled human trials of its own ^[6]. Its molecular weight is roughly 889 Da against the parent protein's ~4963 Da. It is prohibited in sport by the World Anti-Doping Agency, and it is not an FDA-approved drug. Those facts open the reading, not bury it. What follows is the mechanism, the full research summary, the anti-inflammatory and anti-fibrotic findings, TB-500 dosage in the research literature, and the TB-500 legal status. The TB-500 fibrosis research page collects the pathway evidence, while TB-500 side effects and safety signals are answered directly in the FAQ.

How TB-500 works: actin sequestration

TB-500 carries the WH2-type actin-binding motif of thymosin beta-4. X-ray crystallography of a gelsolin-domain-1–thymosin beta-4 hybrid bound to actin, solved to 2 Å, established that the parent peptide forms a 1:1 complex with monomeric G-actin and sequesters it by capping both ends, preventing polymerization ^[1]. That is the molecular job: hold a buffered pool of unpolymerized actin and regulate the cytoskeletal scaffold that drives cell migration.

In injury models, thymosin beta-4 and its LKKTETQ region are associated with accelerated cell migration, angiogenesis, anti-inflammatory and anti-apoptotic signaling, fewer scar-forming myofibroblasts, and recruitment of progenitor cells ^[5]. The seven-mer in TB-500 is the actin-binding handle of that biology. Whether it reproduces the full protein's signaling at the doses used in peptide research has not been shown in controlled human trials. For the how TB-500 works detail — including the cardiac PINCH–ILK–Akt pathway and the angiogenesis signaling — see the research page.

TB-500 as a research peptide

The TB-500 peptide is supplied as a lyophilized powder for laboratory and veterinary research, reconstituted in bacteriostatic or sterile water and kept refrigerated ^[16]. As a short acetylated peptide it is more chemically robust than the full-length protein, but it is still subject to proteolysis and freeze–thaw degradation, and the identity, purity and correct sequence of unregulated research-grade material are a recurring concern ^[17].

The TB-500 peptide is the analytical and anti-doping referent — equine and human LC-MS detection methods characterize the heptapeptide and its metabolites, not the parent protein ^[13]. This matters for interpretation: a result attributed to "TB-500" in a sport-science or detection context is about the fragment, while a result attributed to "thymosin beta-4" in a wound-healing or cardiac study is usually about the full protein. The digest keeps the two apart on every page. The detection work exists because of the compound's WADA-prohibited status in sport, which makes the fragment an anti-doping target in its own right.

What TB-500 has been studied for

Across animal and in-vitro models, thymosin beta-4 (and its LKKTETQ region) has been studied for wound and tissue repair, angiogenesis, cardiac and neurological recovery, hair growth, and anti-inflammatory and anti-fibrotic effects ^[5]. The strongest discrete numbers are preclinical: in a rat full-thickness wound model, topical or intraperitoneal thymosin beta-4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline ^[3]. In mice, the protein activated integrin-linked kinase and Akt and improved cardiac function after coronary artery ligation ^[2].

These are framed as studied effects, not benefits, and almost all of them used the full-length protein. There are no human efficacy trials of the TB-500 heptapeptide for any indication ^[6]. The honest summary is a split one: a reproducible animal-model and in-vitro record for thymosin beta-4, and an unproven translation to the isolated fragment in humans. The recovery interest in TB-500 also draws on thymosin beta-4's characterization as an exerkine — a signaling factor released with exercise — though that, too, is parent-protein biology.