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TB-500

Written by The Peptide Record editorialClinical review not yet completedLast reviewed 15 September 2026Funding No vendor payment

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.

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On this page

  1. What it is, and the naming problem
  2. The real human trial evidence — for a different molecule
  3. Legal status
  4. What this means for safety claims

In brief

Should you care? Yes — this is the single most important thing to know before buying "TB-500." The trial evidence people cite for it was run on a chemically different, larger molecule.

The short version

  • Thymosin beta-4 (Tβ4) is a naturally occurring 43-amino-acid protein, studied by RegeneRx in real human trials.
  • "TB-500" as commonly sold is a synthetic 7-amino-acid fragment of that protein — a different, smaller molecule with no published human trial data of its own.
  • Not a lawful supplement ingredient either way.

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) was one of 12 peptides FDA removed from Category 2 in April 2026, and — like BPC-157 — it went further at the FDA's Pharmacy Compounding Advisory Committee meeting on 23–24 July 2026: the committee voted 8-6 with one abstention to recommend it for the Section 503A bulks list, the same day it made the identical recommendation for BPC-157, despite FDA's own staff having recommended against inclusion beforehand. See BPC-157's legal status for what a PCAC recommendation does and doesn't mean — the short version is that it is advisory only, and as of this page's last review the FDA has not taken the further rulemaking step that would actually place TB-500 on Category 1.

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."

What you can do next

References

  1. RegeneRx Biopharmaceuticals, Phase II venous stasis ulcer trial results announcement, 26 March 2009; trial registered as ClinicalTrials.gov NCT00832091. This result comes from the company's own announcement rather than a peer-reviewed published paper, which is a meaningfully weaker form of evidence and is described here as company-reported for exactly that reason.
  2. Malinda et al., "Thymosin β4 Accelerates Wound Healing," J Invest Dermatol 1999;113(3):364-368, PMID 10469335 — a rat wound-healing model, not a human trial.
  3. FDA, Pharmacy Compounding Advisory Committee meeting, 23–24 July 2026; TB-500 recommended for the Section 503A bulks list 8-6 with one abstention on 23 July. Independently corroborated by contemporaneous reporting from the American Journal of Managed Care ("FDA Panel Backs 6 Peptides for Compounding"), the National Community Pharmacists Association, and law-firm regulatory trackers (Mintz, McDermott Will & Emery, Buchanan Ingersoll & Rooney), all citing the same vote count and noting FDA staff had recommended against inclusion beforehand.