Thymosin beta-4 is a 43-amino-acid peptide your own cells already make. It is the most abundant member of the beta-thymosin family in mammalian tissue and the main molecule that holds onto monomeric (G-)actin inside cells, which is why it shows up in almost every tissue and in wound fluid. The actin-sequestering role is the textbook starting point, but most of the interest in it comes from what happens when that actin pool gets released or remodeled during injury.
A seven-amino-acid stretch in the middle of the molecule, the sequence Ac-LKKTETQ (residues 17–23), carries much of its activity. That fragment is the basis of the research chemical sold online as TB-500, which is a synthetic actin-binding fragment, not the full-length peptide. People often use the two names interchangeably. They are not the same molecule.
What the research actually shows
In animal wound-healing models, topical or injected thymosin beta-4 sped up reepithelialization and increased collagen deposition and new blood vessel growth. One frequently cited dermal study reported reepithelialization roughly 42% higher than saline controls at four days and up to 61% higher at seven days. A 2005 review in *Annals of the New York Academy of Sciences* frames it as "the major actin-sequestering molecule in eukaryotic cells" with a key role in dermal and corneal wound healing, and floats possible uses after hypoxic injuries like heart attack and stroke.
The human data are narrower but real, and most of it is ophthalmic. The biotech RegeneRx developed a preservative-free eye drop, RGN-259, with thymosin beta-4 as the active ingredient. A Phase 2 trial in severe dry eye reported a 35.1% reduction in ocular discomfort (P = 0.0141) and a 59.1% reduction in total corneal fluorescein staining (P = 0.0108) versus vehicle at day 56. Results in the larger Phase 3 dry-eye and neurotrophic-keratopathy programs have been mixed: some trials hit endpoints, at least one European trial did not reach statistical significance on complete corneal healing at four weeks. The drug has not been approved.
The cardiac story is mostly preclinical and early-stage. An injectable form, RGN-352, ran a Phase 2 study in patients after acute myocardial infarction (NCT01311518), and more recent work includes recombinant human thymosin beta-4 trials in China. Proposed mechanisms there are anti-inflammatory, anti-apoptotic, anti-fibrotic, and pro-angiogenic, which is consistent with the wound-healing biology but not a substitute for finished, positive human outcomes.
No regulator has approved thymosin beta-4 (or TB-500) as a drug for any of these uses. Material sold for research is not approved for human consumption, and nothing here is medical or dosing advice.
WADA status
If you compete in tested sport, this one is straightforward. TB-500 and thymosin beta-4 are prohibited at all times under Section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) of the WADA Prohibited List, and have been listed since 2011. They are treated as non-Specified Substances, and at least one athlete has drawn a four-year ban. The prohibition reflects a presumed tissue-repair benefit, not a proven performance effect.
The buyer's problem: what's actually in the vial
Research-grade thymosin beta-4 and TB-500 are sold by many suppliers with little consistency. Because the active sequence is short and well known, identity and purity are the things worth checking, not marketing copy. A serious vendor should provide a third-party certificate of analysis (COA) with mass spectrometry confirming the correct molecular identity and HPLC showing purity, ideally from a lab unaffiliated with the seller. peptideone aggregates public COAs and independent vendor ratings so you can compare what suppliers actually disclose. We do not sell anything or run our own tests. Treat any vendor that can't show batch-level identity and purity data as unverified.