TB-500 is not FDA-approved, came off FDA’s Category 2 table in April 2026 and has no human exposure data, FDA says. What the full-length thymosin beta-4 trials found, and why they are not TB-500 trials.
Last checked 6 min read · 6 sources No paid links in this article Education, not medical advice
TB-500 is not an FDA-approved drug and, as of October 9, 2026, is not on the list of bulk substances 503A pharmacies may compound. FDA moved it off its Category 2 table in April 2026 after its nomination was withdrawn, but says it found no human exposure data for TB-500 drug products. The human trials people cite tested full-length thymosin beta-4, a different molecule.
TB-500 is not an FDA-approved drug, and as of October 9, 2026 the regulation listing bulk ingredients that 503A pharmacies may compound, 21 CFR 216.23, names no peptides (eCFR).
FDA lists “thymosin beta-4, fragment (LKKTETQ), also known as TB-500” among substances that were in Category 2 until their nominations were withdrawn, and says it has not identified any human exposure data for drug products containing it (FDA). Evidence: D.
FDA describes TB-500 as a seven-amino-acid fragment of thymosin beta-4 (LKKTETQ). Thymosin beta-4 itself is a 43-amino-acid protein. Results from trials of the full protein cannot be assumed to apply to the fragment. For the chemistry, see thymosin beta-4 vs TB-500 and our TB-500 reference page.
| Trial | Product and route | People | Main result | Grade |
|---|---|---|---|---|
| Dry eye, phase 2 (2015) | 0.1% thymosin beta-4 eye drops, 28 days | 72 | Neither primary endpoint differed from placebo; some secondary measures improved; no adverse events observed | C |
| Heart attack after stenting (2025) | Recombinant thymosin beta-4 | 96 | Infarct size was smaller in a subgroup dosed within 8 hours, but not in the whole group | C |
| Venous leg ulcers (2007) | Topical thymosin beta-4 | Planned 72; 21 enrolled in the first dose group when reported | Interim design and safety report | D |
Sources: Sosne 2015, Zhang 2025, Guarnera 2007. None of these tested TB-500, and none tested injected TB-500 for muscle or tendon injuries.
Recruiting now: 1 open registration for TB-500 in the Trial Finder.
In July 2026 an FDA advisory committee voted 8 to 6, with one abstention, to recommend adding TB-500 to the 503A bulks list. The vote is advisory; FDA adds substances by rulemaking, and as of October 9, 2026 it had not done so. Full timeline: Is BPC-157 legal now?.
FDA’s safety summary for TB-500 cites a possible risk of immune reactions for certain routes, aggregation and peptide-related impurities, and a lack of information on whether it would cause harm in humans (FDA). Products sold as “research use only” are not compounded prescriptions or approved drugs.
No. TB-500 is not an FDA-approved drug, and as of October 9, 2026 it is not on the 503A bulks list in 21 CFR 216.23.
No. FDA lists it among substances whose nominations were withdrawn from Category 2 (page current as of April 22, 2026), and keeps its safety summary beside it.
FDA says it has not identified any human exposure data for TB-500 drug products. The human trials usually cited tested full-length thymosin beta-4, a different molecule.
An advisory committee voted 8 to 6 in July 2026 to recommend adding TB-500 to the 503A bulks list. That is a recommendation, not an approval, and FDA had not acted on it as of October 9, 2026.
Medical Disclaimer: This is general education, not medical advice. Researched and written by Kymata Health Editorial; sources cited inline. TB-500 is not an FDA-approved drug. Nothing here is a recommendation to use it. Regulatory facts are quoted from FDA and the eCFR and are not graded. Evidence grades: A = several randomized trials or a meta-analysis; B = at least one randomized trial; C = small or pilot human data, expert consensus, or mechanism only; D = animal or cell data, or anecdote.