What it is

Thymosin beta-4 is a 43-amino-acid protein found in nearly every cell, where it holds actin, the protein that forms the cell skeleton. TB-500 is the name used for synthetic material based on it. Products vary: some are the full-length sequence and many are the short actin-binding fragment, amino acids 17 to 23.

How it works

By binding G-actin, thymosin beta-4 controls how quickly cells can build and break down their internal skeleton, which affects cell migration. Studies link it to new blood-vessel growth, reduced inflammation and less scar formation.

What the research shows

Animal studies report faster wound, corneal and heart-tissue repair with thymosin beta-4.
A prescription eye-drop form of full-length thymosin beta-4 (RGN-259) has been tested in human trials for dry eye and corneal wounds.
No controlled human trials exist for the short TB-500 fragment sold as a research peptide.

Regulatory status

Not FDA-approved. In July 2026 the FDA's Pharmacy Compounding Advisory Committee voted 8 to 6 to recommend TB-500 for the compounding bulks list. On October 28, 2026, the Department of Health and Human Services announced an interim enforcement discretion policy covering TB-500 and five other peptides: it does not intend to take action against state-licensed pharmacies, federal facilities or licensed physicians that compound them under section 503A, as long as strict conditions are met. These include bulk material from an FDA-registered manufacturer with a certificate of analysis, a single active ingredient, only the routes of administration the policy lists, specific labeling and reporting of serious adverse events to the FDA. The policy does not add TB-500 to the 503A bulks list or approve any product, it does not cover 503B outsourcing facilities, and HHS says it may revisit the policy if safety or quality problems arise. Research-grade material is not a compounded drug product. It is prohibited in sport by the World Anti-Doping Agency.

Storage and handling

Lyophilized (freeze-dried) powder is most stable sealed, dry and protected from light. Laboratory practice is to keep unopened vials frozen at about -20 °C for long-term storage, or refrigerated at 2 to 8 °C for shorter periods. After reconstitution, keep the solution refrigerated at 2 to 8 °C, avoid repeated freeze-thaw cycles and use aseptic technique for every draw. Formal stability data in solution has not been published for most research peptides, so follow the supplier's label and certificate of analysis.

Reconstitution math

To work out concentration, volume and U-100 syringe units for any vial size, use the reconstitution calculator with TB-500 selected. Always confirm the vial content against the label and the batch's certificate of analysis.

Key references

Goldstein AL et al. Thymosin β4: a multi-functional regenerative peptide. Expert Opin Biol Ther. 2012.
Search PubMed for TB-500 studies

Educational content only

Peptide Knowledge is an educational reference. Nothing on this site is medical advice, a treatment recommendation or dosing guidance. Many compounds described here are not approved for human use and are sold for laboratory research only. Talk to a licensed clinician before starting, stopping or changing any medication or supplement.

TB-500