Description
Test Result: TB500
TB-500 is a synthetic peptide fragment of thymosin beta-4 (also called Tβ4 or TB4), a naturally occurring 43-amino-acid protein found in nearly every cell. Specifically, the form identified in analytical and anti-doping work is the N-acetylated heptapeptide Ac-LKKTETQ (residues 17–23 of thymosin beta-4), which includes the actin-binding region of the parent protein.
It is not the same molecule as full-length thymosin beta-4. Most published human research has been conducted on the full protein (or topical formulations of it), not the short fragment sold as TB-500. The two can differ in pharmacokinetics, activity, and safety profile.
Mechanism
Thymosin beta-4 sequesters monomeric G-actin, helping regulate the cytoskeleton, cell shape, and migration. The LKKTETQ motif is the key actin-binding segment. Related effects observed in laboratory and animal studies include promotion of cell migration, angiogenesis (new blood vessel formation), modulation of inflammation, and support for tissue repair processes. Some activity may also involve metabolites of the fragment rather than the intact peptide itself.
Research and Evidence
- Animal and in vitro data: Studies on thymosin beta-4 (and to a lesser extent related fragments) show accelerated wound closure, reduced inflammation/scarring, corneal healing, and cardioprotective effects in rodent models of injury or ischemia.
- Human data: Limited and primarily on full-length thymosin beta-4 in specific formulations (e.g., topical gels for leg ulcers or eye drops for dry eye), with mixed results. FDA reviews have found no human exposure data for the TB-500 fragment itself, and no completed published randomized controlled trials evaluating the marketed fragment for musculoskeletal recovery, wound healing, or other common claimed uses.
- It gained early attention as a veterinary product used in racehorses and greyhounds; anti-doping labs developed detection methods for it around 2011–2012.
Promotional claims (faster recovery from tendon/ligament/muscle injuries, reduced inflammation, general healing) largely extrapolate from animal data on the parent protein or rely on anecdotal reports. It is frequently discussed or “stacked” with BPC-157.
Regulatory and Legal Status (as of October 2026)
- Not FDA-approved for any human use. No approved drug product exists.
- Compounding: It was previously on the FDA’s Category 2 list (substances with significant safety concerns that could not be compounded). It was removed from Category 2 in April 2026 after nomination withdrawal. In July 2026, the Pharmacy Compounding Advisory Committee voted 8–6 (with one abstention) to recommend it for the 503A bulk drug substances list for wound healing—against the recommendation of FDA staff, who cited lack of human data. The vote is advisory only; formal rulemaking has not been completed, so lawful compounding is not yet authorized.
- Sold online mainly as a “research use only” chemical. Product identity and purity can vary; some vials labeled TB-500 may contain full-length thymosin beta-4 instead.
- Sports: Prohibited at all times by the World Anti-Doping Agency (WADA) under section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), specifically listed as “Thymosin-β4 and its derivatives e.g. TB-500.” Detection methods exist for urine testing.
Safety Notes
Formal safety data for the fragment are very limited. Anecdotal reports include injection-site reactions, transient fatigue/lethargy, headache, and mild nausea. Theoretical concerns exist around cell migration/angiogenesis in the setting of active or prior malignancy. Risks also include impurities, aggregation, or mislabeled products from unregulated sources. Full-length thymosin beta-4 has been studied in small human trials (mostly topical or short-term) and was generally well tolerated in those settings, but that does not directly establish safety for systemic use of the fragment.
