TB-500: What It Is and What Is Known

Thymosin beta-4 is a protein found in many of the body's cells. It plays a role in how cells move and in tissue repair processes.

TB-500 is a synthetic peptide based on a short section of thymosin beta-4. FDA's review identifies it as a fragment of thymosin beta-4 with the sequence LKKTETQ. It is a different substance from the full protein.

The full thymosin beta-4 protein has been tested in some human clinical trials, for example in eye-drop studies. No thymosin beta-4 product has been approved by the FDA.

Research on TB-500 itself comes mostly from laboratory and animal studies. FDA has stated that it did not identify any human exposure data for drug products containing this fragment.

TB-500 is not FDA-approved. That means the FDA has not reviewed evidence that it is safe and effective for any condition.

In its review of substances nominated for use in compounding, FDA raised concerns about the peptide's potential to clump together (aggregation) and about peptide-related impurities, and said it lacks important information about safety issues this substance may raise.

TB-500 is not on FDA's list of bulk substances that pharmacies may use to compound medications. An FDA advisory committee discussed it in July 2026. As of November 2026, FDA had not published a final decision.

The World Anti-Doping Agency prohibits TB-500 and thymosin beta-4 at all times, in and out of competition, in class S2 (peptide hormones, growth factors, related substances, and mimetics).

If you are subject to drug testing in your sport, check with your anti-doping organization before using any product.