A product sold for injury recovery that contains a short fragment of thymosin beta-4, a natural protein that controls the cell skeleton and helps wounds close. The healing evidence belongs to the full-length protein in eye, skin, and heart studies rather than to the fragment, and the FDA has found no human exposure data for TB-500 at all.
Thymosin beta-4 is the main actin-sequestering molecule in cells, which means it holds a reserve of the protein cells use to build their internal skeleton and move. By controlling actin it helps cells migrate into a wound, and in animal and cell models the full protein promotes new blood vessels, collagen deposition, and keratinocyte and endothelial cell movement while dampening inflammation. The short sequence LKKTETQ, positions 17 to 23 of the protein, is the actin-binding site. TB-500 is that sequence with an acetyl group added to one end.
Injected as TB-500 (1/7)
TB-500 is LKKTETQ, a short stretch of thymosin beta-4 with an acetyl cap.
Whether the fragment reproduces the protein's effects in people has not been shown, and the claims attached to TB-500 are the claims made for full-length thymosin beta-4. Even the full protein's human record is mixed: a 72-subject dry eye trial missed both primary endpoints while improving some secondary ones, a 73-patient venous ulcer trial suggested faster healing at one dose, and a 96-patient heart attack trial found smaller infarcts only in the subgroup dosed within 8 hours. The fragment is cleared and metabolized quickly enough that detection methods focus on its breakdown products. No study measures what it does in human tissue.
TB-500 is sold online for tendon, ligament, and muscle injuries, and is used by athletes and in racehorses. The product contains a short piece of thymosin beta-4, the segment responsible for binding actin, which vendors claim promotes blood vessel growth, cell migration, collagen deposition, and lower inflammation. Human trials have tested only the full-length protein: eye drops for dry eye and nonhealing corneal defects, a gel for venous leg ulcers, and an intravenous version after heart attack. None of them tested a TB-500 fragment, and none involved sports injuries.
The compound first drew attention as a veterinary preparation given to horses, and doping-control laboratories built tests to detect it in equine blood and urine. The FDA says it has identified no human exposure data for drug products containing the thymosin beta-4 fragment and lacks information on whether it would cause harm, and its advisory committee is scheduled to discuss TB-500 in July 2026. The World Anti-Doping Agency prohibits thymosin beta-4 and its derivatives, naming TB-500 specifically. Regulators in Australia and Canada list it among unapproved injectable peptides sold online.
Every human study involves full-length thymosin beta-4 or a named investigational product rather than TB-500. Those include a randomized phase 2 dry eye trial of 72 subjects, nine compassionate-use patients with neurotrophic corneal defects, a placebo-controlled venous ulcer study of 73 patients, and a 2025 randomized trial of recombinant thymosin beta-4 in 96 heart attack patients. The TB-500-specific literature consists of analytical chemistry: identification of the acetylated fragment in a doping product and detection methods for horses. Preclinical work on the protein is broad.
The core unknown is identity: whether any real-world TB-500 vial matches a studied material, and whether a short fragment does what the whole protein does. No outcome data exist for the recovery uses it is sold for. Safety questions about immunogenicity, aggregation, and impurities are unanswered because no one has looked. The FDA's July 2026 advisory discussion concerns compounding rather than approval.
No human safety data for TB-500 exist, because no human study of the fragment has been published. In the full-protein trials, eye drops caused no adverse events in 72 subjects, and the topical ulcer treatment had a safety profile comparable to placebo. The FDA warns that compounded TB-500 may pose a risk of immune reactions from aggregation and peptide impurities and that it has no human exposure data to judge harm. Injecting an unverified product adds risks of contamination and wrong dose.
No regulator has approved this compound, and no company is seeking approval.
TB-500 is not approved by the FDA or any other regulator. The FDA lists compounded drugs containing the LKKTETQ fragment of thymosin beta-4, which is what TB-500 contains, among bulk substances that may present significant safety risks, and its Pharmacy Compounding Advisory Committee is scheduled to discuss TB-500 free base and acetate on July 23, 2026. The World Anti-Doping Agency prohibits thymosin beta-4 and its derivatives such as TB-500 at all times. Australia's TGA and Health Canada name it among unapproved injectable peptide products.