TB-500
Thymosin beta-4 fragment, LKKTETQ
A seven amino acid fragment of a repair protein, injected for healing.
TB-500 is sold to athletes and gym users for tendon, muscle and ligament repair, and is banned in sport as a growth factor. It carries the stretch of thymosin beta-4 thought to do the healing, but the single published test of that found it did not close wounds. FDA could not find one pharmacy compounding it or one human who had been given it in a published study.
Where it stands, jurisdiction by jurisdiction
United States
Unregulated, unregulated, sold anywayDecided on: Precaution, Contested
Not a lawful dietary ingredient and not on the 503A list. Nominated as a 3 milligram per milliliter injection for wound healing, without the nominator ever specifying what kind of wound. FDA found no human study by any route, no animal toxicity studies, and one laboratory experiment in which TB-500 failed to close scratch wounds in cultured fibroblasts. The only pharmacokinetic data in existence come from thoroughbred geldings. The advisory committee recommended adding it 8 to 6 with one abstention on 23 July 2026, against the agency's proposal, and it remains off the list.
Regulatory positions change, sometimes quickly. Check the date on a source before relying on it.