Thymosin beta-4 is a ubiquitous actin-sequestering protein that modulates cell migration and proliferation during wound healing and tissue repair in animal models.
Peptide reference
TB-500
TB-500
In vitroHow it works
TB-500 is a grey-market name, not one molecule. A vial may hold full-length synthetic thymosin beta-4 (43 amino acids) or short fragments of it. Thymosin beta-4 is a protein that binds actin, which helps cells move during tissue repair. In animals it speeds wound healing, calms inflammation and helps grow new blood vessels. Almost all of that research used the full-length protein. No human trial of any version has tested tendon repair.
Key studies
Safety
WADA Prohibited List 2026. No long-term human safety data. The immunomodulatory and angiogenic mechanisms are well-established in animals; human extrapolation remains speculative.
Frequently asked
What is TB-500?
TB-500 is a grey-market name, not one molecule. A vial may hold full-length synthetic thymosin beta-4, a 43-amino-acid peptide, or a short fragment of it. Almost all published research used the full-length peptide. Thymosin beta-4 binds actin inside cells and helps regulate the cytoskeleton. In animal wound models it's linked to cell migration, blood vessel growth, and inflammation resolution. Human mechanistic data for tendon repair doesn't exist.
Does TB-500 actually heal tendons?
No human tendon trial of TB-500 has been registered or published. The tendon-specific evidence is a 2020 lab study growing cells on a scaffold, not an injection into a human tendon. The animal data showing tissue-repair signal doesn't have a human tendon result attached to it yet.
Is TB-500 approved by the FDA?
No. TB-500 has no FDA-approved drug application. On July 23, 2026, the FDA's Pharmacy Compounding Advisory Committee (PCAC) recommended inclusion of TB-500 on the 503A Bulk Drug Substances List, the list that covers pharmacy compounding. That's an advisory vote, not an approval, and FDA final action is pending. Outside that process, TB-500 is sold as a research chemical.
Is TB-500 banned for athletes?
Yes. TB-500 falls under WADA's S2 category covering growth factors and substances that affect muscle, tendon, and vascular regeneration, and it's prohibited at all times. Athletes subject to WADA testing should treat it as banned in and out of competition, regardless of how the FDA's compounding review turns out.
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