Independent. No paid placement. Reviewed weekly Editorial policy Newsletter

Home›The Library›Thymosin beta-4

Thymosin Beta-4 (full-length)

Written by The Peptide Record editorialClinical review not yet completedLast reviewed 12 September 2026

This is a case where the honest answer is "tested properly, and the results are genuinely mixed" — not "untested," and not "proven." An early placebo-controlled trial in a rare eye condition showed a positive trend that didn't reach statistical significance; a larger, later confirmatory trial of the same drug, in a similar condition, missed its primary endpoint entirely in 2026.

On this page
  1. What it is, and how this page differs from TB-500's
  2. The trial evidence
  3. Separately: the wound-healing data
  4. Legal status

In brief

Should you care? Yes if you've read TB-500's page — this is the real, larger protein behind that naming confusion, with its own genuine, and genuinely mixed, human trial history.

The short version

  • The natural, full-length protein — a different, larger molecule than the synthetic fragment sold as "TB-500."
  • A real Phase 3 ophthalmic trial trended positive but missed statistical significance.
  • A larger 2026 confirmatory trial of the same drug missed its primary endpoint outright.

What it is, and how this page differs from TB-500's

Thymosin beta-4 (Tβ4) is the naturally occurring 43-amino-acid actin-binding protein that this site's TB-500 page explains is a chemically distinct, larger molecule than the synthetic 7-amino-acid fragment sold under that name. This page covers the real human trial history of the full-length protein itself, developed clinically by RegeneRx (as RGN-259, an ophthalmic solution) and its licensees.

The trial evidence

RGN-259's Phase 3 trial in neurotrophic keratopathy (Sosne, Kleinman, Springs, Gross, Sung, Kang, Int J Mol Sci 2023;24(1):554, DOI 10.3390/ijms24010554) found complete corneal healing in 6 of 10 RGN-259-treated patients versus 1 of 8 on placebo at 4 weeks — a real, randomized, double-masked, placebo-controlled trial, though the primary result (p=0.0656) did not reach conventional statistical significance. A later, larger confirmatory Phase 3 trial (SEER-3, run by ReGenTree/HLB Therapeutics) missed its primary endpoint in a July 2026 announcement, reportedly due to an unexpectedly strong placebo response. That's a real, negative finding, and it shouldn't be left out just because the earlier trial trended positive.

Separately: the wound-healing data

A topical Tβ4 gel (RGN-137) showed company-announced Phase 2 results in venous stasis ulcers in 2009 — the same source already cited, with the same caveat that it's a company announcement rather than a peer-reviewed publication, on this site's TB-500 page. It's repeated here because it's directly relevant to full-length Tβ4's own evidence base, separate from the naming confusion with "TB-500."

Legal status

Neither the ophthalmic (RGN-259) nor topical (RGN-137) formulations are FDA-approved. Full-length Tβ4 is not a lawful dietary-supplement ingredient, and it is not the version sold as "TB-500" — see that page for the distinction.

References

  1. Sosne, Kleinman, Springs, Gross, Sung, Kang, "0.1% RGN-259 (Thymosin β4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial," Int J Mol Sci 2023;24(1):554, DOI 10.3390/ijms24010554.
  2. SEER-3 missed-primary-endpoint announcement, reported by Ophthalmology Times, 5 July 2026 — a company announcement, not itself a peer-reviewed paper.