# TB-500: Research Overview — Agility Peptide > A literature summary of TB-500 (Ac-LKKTETQ), a synthetic fragment of thymosin beta-4 studied for tissue repair. Covers the fragment-versus-full-protein distinction, actin biology, and key safety signals. The short Ac-LKKTETQ peptide holds the actin-binding motif of thymosin beta-4 — but most of the efficacy evidence was generated using the full 43-amino-acid parent protein, not the fragment itself. ## The short version TB-500 is a synthetic peptide just seven amino acids long, with the sequence Ac-LKKTETQ. That stretch is the *actin-binding* region of a larger natural protein called thymosin beta-4. Actin is a core component of the internal skeleton cells use to hold their shape and migrate toward a wound, so the parent protein is closely linked to cell movement, repair-signal cascades, and new blood-vessel growth [10]. The single most important fact about TB-500 is a naming gap. In commerce and in anti-doping labs, "TB-500" denotes the short seven-amino-acid fragment. But most published *efficacy* research used full-length thymosin beta-4, which is roughly five times larger (~4,963 Da versus ~889 Da for the fragment) [8]. It is not established that the fragment reproduces what the whole protein does at the doses used in peptide research. TB-500 is not an approved medicine, is banned in sport by WADA, and this page reports doses only as studied — never as advice. ## What it is TB-500 is a synthetic, N-terminally acetylated heptapeptide with the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, corresponding to residues 17-23 of thymosin beta-4 (Tβ4), a 43-amino-acid protein encoded by TMSB4X. This `LKKTETQ` stretch is the conserved actin-binding (WH2) motif shared across the beta-thymosin family. The size distinction matters throughout: the marketed fragment is ~889 daltons; full-length Tβ4 is ~4,963 daltons. In anti-doping matrices and commercial supply, "TB-500" unambiguously refers to the heptapeptide. In most of the published repair literature, the compound tested was the intact protein. Wherever a finding below used full-length Tβ4 rather than the 7-mer, this page flags it — because that is exactly where TB-500 marketing borrows a larger molecule's evidence base [8]. ## How it works Full-length thymosin beta-4 is the body's major intracellular *G-actin sequestering* peptide. "G-actin" is the free, single-unit (globular) form of actin; sequestering means Tβ4 grabs and holds those monomers to maintain a buffered pool of unpolymerized actin, regulating the dynamics of the cytoskeleton. A 2-angstrom X-ray crystal structure of a gelsolin-domain-Tβ4 hybrid bound to actin established that Tβ4 forms a 1:1 complex with G-actin and caps both ends of the monomer, preventing polymerization — the structural basis for actin-buffering [12]. Regulating actin dynamics underpins multiple repair processes: faster cell migration into a wound, promotion of new blood-vessel growth, suppression of pro-apoptotic and inflammatory signals, reduced myofibroblast (scar-forming) activity, and recruitment of progenitor cells [10]. A 2012 multi-model review consolidated these activities as the mechanistic rationale for clinical development in dermal wounds, corneal injury, and cardiac and CNS repair [10]. Whether the isolated seven-amino-acid fragment reproduces all of this at research doses has not been established in controlled human trials [10]. ## What the research shows *Structural basis.* Crystallography established the 1:1 G-actin-capping mechanism [12], and a comprehensive review consolidated thymosin beta-4's actin-binding, pro-migratory, anti-scarring, anti-inflammatory and angiogenic activities as the basis for ongoing clinical development [10]. *Human safety (full-length protein).* A randomized, placebo-controlled Phase 1 study gave synthetic thymosin beta-4 intravenously to 40 healthy volunteers — a single dose followed by daily dosing for 14 days at 42, 140, 420 or 1260 mg. The compound was well tolerated, with only infrequent mild-to-moderate adverse events, no dose-limiting toxicities, no serious adverse events, and dose-proportional pharmacokinetics [11]. Note: this was full-length Tβ4, not the TB-500 fragment. *Animal dose-response.* In male Wistar rats with embolic stroke, intraperitoneal thymosin beta-4 (2, 12 or 18 mg/kg, starting 24 hours post-stroke) improved neurological function at 2 and 12 mg/kg — but 18 mg/kg gave no significant benefit, a non-monotonic result where more was not better [9]. *Field-level review.* A 2026 Sports Medicine narrative review listing TB-500/thymosin beta-4 and BPC-157 among unapproved musculoskeletal peptides concluded that favorable animal-model outcomes have not been matched by rigorous human safety data, that the potential for serious harm exists, and that these compounds operate largely outside regulatory oversight [8]. ## Reported effects, cautions & safety The cautions for TB-500 are unusually concrete and several are compound-specific: - *Identity gap.* Because "TB-500" is the fragment but most efficacy data are from full-length Tβ4, efficacy claims for the fragment in humans are unproven. No completed controlled clinical trial of the TB-500 fragment exists for any indication [8]. - *Tumor and angiogenesis signal.* Thymosin beta-4 is overexpressed in several cancers (including pancreatic and colorectal) and is implicated in tumor angiogenesis and metastasis; the same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression [10]. - *Mixed preclinical results.* In dystrophin-deficient mice, chronic Tβ4 increased regenerating fibers but did not improve muscle strength, cardiac function or fibrosis, and systemic Tβ4 failed to reduce ischemia-reperfusion injury in a porcine cardiac study [8][10]. - *Non-monotonic dose-response.* The rat stroke study's finding that 18 mg/kg was no better than 12 mg/kg undermines community "loading" rationales directly — higher is not always better [9]. - *Regulatory status.* TB-500 is prohibited in sport by WADA and classified as a prescription medicine in some jurisdictions; it has appeared as a designer doping agent in racehorses, prompting dedicated detection methods in equine and human anti-doping assays [8]. No community-anecdote reports are compiled in this desk's source material for TB-500 as a standalone compound; the cautions above are drawn from the cited literature. ## Where it fits in recovery research TB-500 occupies a specific niche on this desk: a compound whose *mechanism* — actin regulation driving cell migration and angiogenesis — is well described at the protein level, but whose *evidence as the actual fragment sold* is the thinnest of the four [8]. Where [BPC-157](/bpc-157) leads with a direct angiogenesis mechanism and [GHK-Cu](/ghk-cu) leads with matrix synthesis and human topical data, TB-500's story is largely thymosin beta-4's story, borrowed. That makes it the clearest case on the desk for why careful reading of what was actually tested matters. See how it lines up on the [comparison page](/compare). ![TB-500 research illustration](/images/tb-500.webp) --- Peer-reviewed data, plain-English summaries — a research digest, not a dose guide and not a product for sale.