TB-500

A short, lab-made piece of thymosin beta-4, a natural 43-amino-acid protein involved in cell movement and repair. It copies residues 17–23, the protein's actin-binding motif.

The parent protein, thymosin beta-4, is the main protein that holds single actin units inside cells, which supports cell migration and, in animals, blood-vessel growth and wound repair. The LKKTET stretch in this fragment is the conserved actin-binding motif. Much of the full protein contacts actin, so the fragment may not reproduce the whole protein's activity.

There are no human studies of TB-500 itself, no human pharmacokinetic data and no FDA adverse-event reports for it alone. The full-length protein has been tested in people (RGN-259, including phase 3 dry-eye trials) without leading to approval, and none of those results apply to the fragment. In animal and cell work, a non-acetylated version aided wound healing in aged mice, while TB-500 did not significantly speed wound closure in cultured skin cells. Whether the fragment reproduces the parent protein's effects in living animals is not known.

Human safety is unknown because there are no human studies. FDA cites immune-reaction and aggregation risk with research-grade peptides, and the certificates it reviewed lacked identity, assay and endotoxin results. One FDA adverse-event case of skin and gum darkening involved a BPC-157/TB-500 blend, so the cause can't be assigned to either peptide; no repeat-dose, genetic, reproductive or cancer toxicity studies exist.

Not FDA-approved for any use. It was on FDA's Category 2 safety list from 2023 until April 2026. In July 2026 FDA's Pharmacy Compounding Advisory Committee voted 8–6–1 to recommend adding it to the 503A bulks list for wound healing; the vote is advisory, no final rule had been issued as of October 2026, and it concerns pharmacy compounding, not research-grade material. WADA prohibits it at all times (S2).