What it is
TB-500 is a synthetic fragment of thymosin beta-4, a natural protein found in almost all cells. Thymosin beta-4 helps cells move and helps build new blood vessels.
TB-500 is marketed online for injury recovery and flexibility. The full thymosin beta-4 protein and the short TB-500 fragment are not the same thing, and most research used the full protein.
US regulatory status
Not FDA-approved. In April 2026 the FDA removed it from its Category 2 list of compounding substances with safety concerns, and in July 2026 an FDA advisory committee voted 8-6 to recommend adding it to the list of substances pharmacies may compound. As of October 2026 that recommendation is not final: it still needs FDA rulemaking, a proposed interim access policy was under White House review, and it remains an unapproved drug.
What the research shows
Animal and lab studies suggest thymosin beta-4 may help wound, heart and eye healing. Human trials of the full protein (for example, eye drops for dry eye) have shown mixed results. There are no good human trials of TB-500 itself for muscle or tendon injuries.
How it is given
Subcutaneous injection (unapproved)
Commonly reported side effects
- Injection site reactions
- Headache
- Tiredness
- Very limited human safety data
- Risk of contaminated or mislabeled products
Questions to ask your provider
- What does the research really show about TB-500 in humans?
- Are there FDA-approved treatments for my goal that have stronger evidence?
- What are the risks of products labeled "research use only," and how would I know what is really in them?