TB-500

The human trial data used to sell "TB-500" was actually run on a different, larger molecule — full-length thymosin beta-4 — not the short synthetic fragment that vials sold as "TB-500" typically contain. That distinction matters more than almost anything else on this page.

What it is, and the naming problem

Thymosin beta-4 (Tβ4) is a naturally occurring 43-amino-acid actin-binding protein. "TB-500" is a synthetic 7-amino-acid peptide (Ac-LKKTETQ), representing only the actin-binding subdomain of Tβ4 — roughly 843 daltons versus Tβ4's roughly 4,964 daltons. Both work through the same general mechanism (sequestering monomeric actin), but they are chemically distinct molecules, and online sellers routinely use the names interchangeably.

The real human trial evidence — for a different molecule

RegeneRx ran Phase 2 human trials of full-length Tβ4, formulated as a topical gel (RGN-137), in venous stasis ulcers (ClinicalTrials.gov NCT00832091) and pressure ulcers. The company's own March 2009 results announcement reported the treatment was safe and well tolerated at all three dose levels, with the mid-dose level showing more rapid wound-healing initiation than placebo — a company-reported result, not one we've located in a peer-reviewed published paper, which is a meaningfully weaker form of evidence and worth stating plainly rather than dressing up as more than it is. The foundational animal work is peer-reviewed: Malinda et al. found topical or intraperitoneal Tβ4 increased wound re-epithelialization by 42% at 4 days and up to 61% by 7 days in a rat model, versus saline controls (J Invest Dermatol 1999, PMID 10469335). None of this — company-reported or peer-reviewed — is a trial of the synthetic 7-amino-acid fragment actually sold as "TB-500."

Legal status

Neither molecule is FDA-approved for any indication. TB-500 (the fragment) sits on FDA's Category 2 restricted-compounding list; it was reviewed, without a recommendation for inclusion, at the same July 2026 Pharmacy Compounding Advisory Committee meeting that reviewed BPC-157 — see BPC-157's legal status for how that process works.

What this means for safety claims

Because the synthetic fragment has essentially no independent human safety data of its own, none of the tolerability findings from the full-length-protein trials above should be assumed to transfer to what's actually in most vials sold as "TB-500."