TB-500 (thymosin beta-4 fragment)

What it is

Its sequence includes the actin-binding region of thymosin beta-4. That protein binds actin, which cells use to keep their shape and move. FDA notes the added acetyl group may change how it acts, and in one cell study TB-500 itself did not speed wound closure.

What it is studied for

TB-500 has been tested in rats with repaired Achilles tendons, alone and with BPC-157, and on cultured fibroblasts in a wound-closure test. Thymosin beta-4, the full protein, is a separate molecule: in a 72-person dry-eye trial, its eye drops did not beat placebo on the main measures, though some secondary measures improved.

What the evidence says

Animal and cell studies; no human studies

In the small rat study, which used commercially sourced TB-500, it was linked to stronger tendons and better tissue scores after four weeks, and adding BPC-157 gave no extra benefit. In the cell study, TB-500 itself did not speed wound closure. FDA found no human studies of TB-500, so its effects and safety in people are unknown.

How it was studied

FDA found no human studies; in animals, TB-500 was injected under the skin of horses and into the abdomen of rats. Human trials of full-length thymosin beta-4 used eye drops, and no study of TB-500 in a dissolving strip was found.