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TB-500

TB-500 is a lab-made peptide of 7 amino acids, copied from the part of thymosin beta-4 that binds the cell protein actin. Thymosin beta-4 is a 43-amino-acid protein found in many human cells. Products sold as TB-500 are not always the same substance. Human trials, such as eye-drop trials for dry eye, used full-length thymosin beta-4, not TB-500. FDA found no published study in which TB-500 was given to people.

Not approved · research onlyWADA Prohibited at all times (S2, thymosin beta-4 and its derivatives)Checked October 2026
Open the TB-500 calculatorSources

Approval status

Not approved as a medicine in any country. FDA had listed it among compounding substances that may pose significant safety risks, noting there were no human exposure data. It came off that list in April 2026 after its nomination was withdrawn, but it is still not a substance pharmacies may compound with. In July 2026 FDA staff reviewed it for wound healing and advised against allowing it; news reports say FDA's advisory panel narrowly voted to recommend it.145678

What it’s used or studied for

  • Animal & lab only

    Skin wound healing: the same seven-amino-acid sequence, without the acetyl group, sped skin wound repair in aged mice. TB-500 itself did not speed wound closure in a cell study.1910

  • Animal & lab only

    Tendon healing: in a 2026 rat study of repaired Achilles tendons, a peptide described as TB-500 improved tendon structure and strength after four weeks.11

Each label shows how strong the evidence is: an approved use, human studies, animal or lab studies only, or a popular claim with no published studies. Being studied is not the same as being proven safe or effective.

Side effects

There are no published human safety studies of TB-500, and FDA found no adverse event reports for TB-500 on its own. A small trial of full-length thymosin beta-4 eye drops reported them as well tolerated, but that result may not apply to TB-500.112

Cautions

  • FDA warns that injected TB-500 may trigger immune reactions, a risk raised by clumping (aggregation) and impurities.1
  • FDA found different salts and related substances sold under the name TB-500, so products with the same label may differ.1
  • A public certificate of analysis that FDA reviewed for TB-500 did not test for bacterial endotoxins, impurities or clumping.1

Sources

  1. FDA briefing document: Evaluation of TB-500 for the 503A bulks list (PCAC meeting, July 2026)
  2. PubChem: TB-500, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (CID 62707662)
  3. UniProt: Thymosin beta-4, human (P62328)
  4. FDA: Bulk drug substances used in compounding that may present significant safety risks (current as of April 2026)
  5. FDA: Bulk drug substances nominated for compounding under section 503A, categories 1 to 3 (updated May 14, 2026)
  6. FDA guidance: Interim policy on compounding using bulk drug substances under section 503A (January 2025)
  7. AJMC news: FDA panel backs 6 peptides for compounding (July 31, 2026)
  8. World Anti-Doping Agency: 2026 Prohibited List (in force from January 1, 2026)
  9. Philp et al. (2003). Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in diabetic and aged mice. Wound Repair Regen
  10. Rahaman et al. (2024). Quantification of TB-500 and its metabolites and their wound healing activity in vitro. J Chromatogr B
  11. Biçer et al. (2026). Effects of BPC-157 and TB-500 on Achilles tendon healing in rats. Jt Dis Relat Surg
  12. Sosne, Dunn & Kim (2015). Thymosin beta 4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea

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