Thymosin Beta-4

Thymosin Beta-4 has a genuine, multi-decade human clinical trial history and multiple FDA orphan drug designations, but it is not FDA-approved for any use in the United States, or anywhere else we could verify. This page describes its mechanism and real research history — not dosing or usage guidance, and not a recommendation to use it. Talk to a doctor before considering it.

Thymosin Beta-4 (Tβ4, WHO INN "timbetasin") is the native, full-length 43-amino-acid actin-binding protein naturally present throughout the human body — distinct from TB-500, the shorter synthetic fragment/analog of this same protein already covered elsewhere on this site. Where TB-500 is a lab-truncated piece sold as an unregulated research chemical, full-length Tβ4 is the actual endogenous molecule, and it's the version that has gone through formal pharmaceutical development — recombinant and synthetic full-length versions have been manufactured under drug-development programs (e.g., RegeneRx's RGN-259 and RGN-137, and China's NL005) and tested in registered human trials. Its proposed mechanism involves sequestering monomeric actin to regulate cell migration, angiogenesis, and anti-inflammatory and anti-apoptotic signaling — the basis for research into wound healing, corneal and ocular surface repair, and cardiac tissue recovery after ischemia.

Unlike TB-500, full-length Tβ4 has real registered human trials, run under formal FDA and international drug-development programs rather than as a compounding or research-chemical pathway. First-in-human Phase 1 studies (e.g. NCT04555824 and NCT04555850) in healthy volunteers found it generally well tolerated at tested doses. As an ophthalmic solution (RGN-259), it was studied in Phase 2 trials for dry eye disease that showed statistically significant improvement in symptoms like ocular grittiness, and later in three Phase 3 dry eye trials (ARISE-2, ARISE-3, SEER-3) across more than 1,600 patients combined — all of which missed their pre-specified co-primary endpoints, though pooled secondary-endpoint analyses showed some signal on signs and symptoms. A separate Phase 3 trial in neurotrophic keratopathy narrowly missed statistical significance on its primary endpoint (p = 0.0656) but reported a 60% complete-healing rate versus 12.5% for placebo by day 29, reaching significance two weeks later. As a topical gel (RGN-137), it holds FDA orphan drug designation for epidermolysis bullosa and was evaluated in Phase 2 trials showing accelerated wound healing, including a published case of complete healing in one enrolled patient. Separately, intravenous recombinant Tβ4 (NL005) has been studied in China in Phase 1 and Phase IIb trials for acute myocardial infarction, alongside smaller pilot human studies of Tβ4-pretreated cell transplantation after STEMI, building on substantial animal data on cardiac repair. In short: real Phase 1-3 human trials exist across several indications, with some positive and some narrowly-missed results — but no trial has yet produced an approved drug.

Full-length Thymosin Beta-4 is not FDA-approved for any use, and we could not verify an approval anywhere else in the world. Two formulations hold FDA orphan drug designation — RGN-259 for neurotrophic keratopathy and RGN-137 for epidermolysis bullosa — but orphan drug status is an incentive program (tax credits, market exclusivity, fee waivers) to encourage development of rare-disease treatments; it is not marketing approval and does not mean the drug works or is available for prescription. Because full-length Tβ4 has been developed through the standard FDA investigational new drug (IND) and orphan-drug pathway rather than the compounding-pharmacy route, it is a separate regulatory track from the 2026 FDA bulk drug substance actions that affected TB-500, BPC-157, and related peptides — see our Peptides hub page for that broader compounding-list context. As with TB-500 and its other derivatives, full-length thymosin beta-4 is listed under the World Anti-Doping Agency's Prohibited List (Section S2.3, growth factors) and is banned at all times in competitive sport.