A quiet analytical research laboratory at night, racks of glass vials along a dim bench.

Thymosin Beta-4 (TB-500)

Thymosin beta-4 is a naturally occurring 43-amino-acid peptide that has been tested in human trials, notably as RGN-259 eye drops. TB-500 is the name used for synthetic versions and fragments sold as research chemicals; it is unapproved and prohibited in sport. Vegalab does not make, sell or source either.

What thymosin beta-4 is

Thymosin beta-4 (Tβ4, about 4.9 kDa, N-terminally acetylated) is one of the most abundant intracellular peptides and the main G-actin sequestering molecule in cells. Preclinical studies link it to cell migration, angiogenesis and wound repair, and the N-terminal fragment Ac-SDKP has anti-fibrotic activity. The sequence LKKTETQ (residues 17 to 23) is the actin-binding motif that many TB-500 products are based on. It is present at high levels in platelets and white blood cells and released at sites of injury.

Clinical and regulatory status

Tβ4 is not approved as a drug anywhere. RGN-259, a sterile Tβ4 eye drop, has been studied in phase 2 and phase 3 trials for dry eye disease and neurotrophic keratitis, with mixed primary endpoint results. Topical and intravenous formulations were studied earlier for dermal wounds and cardiac indications. FDA placed TB-500 in Category 2 of the interim 503A bulks list in 2023 and announced in April 2026 it would remove it pending review, which affects compounding only. WADA names thymosin beta-4 and its derivatives, such as TB-500, under S2.

Delivery facts

Tβ4 is highly water-soluble and unstructured in solution, which makes it protease-sensitive and gives it a short circulating half-life. Oral delivery is not realistic for the full-length peptide. Local delivery (ocular, topical, wound) is where clinical development has focused, because it avoids systemic clearance. Research-chemical TB-500 products often differ from full-length Tβ4, being short fragments or variants with different properties, and their identity is rarely verified by the seller. Stability in solution is limited, and cold-chain handling matters for any peptide of this type.

Why this page exists

The distinction between a clinically studied peptide and gray-market research chemicals sold under a similar name is important for clinicians and partners. Clinical Tβ4 programs are regulated trials with defined products and endpoints. TB-500 products are research chemicals without quality control or approved use. Treating the two as interchangeable misrepresents the evidence, and it is the main reason this page exists. Clinicians asked about TB-500 should refer to approved therapies.

Key facts

Thymosin beta-4 is a multifunctional peptide studied in dermal, corneal and cardiac repair (Goldstein et al. 2012, Expert Opin Biol Ther 12:37)
Thymosin-beta-4 and its derivatives, e.g. TB-500, are prohibited under S2 peptide hormones, growth factors and related substances (WADA Prohibited List 2026)
RGN-259 (thymosin beta-4 eye drops) has been evaluated in phase 3 ARISE trials in dry eye disease (ReGenTree ARISE program, ClinicalTrials.gov registry)

How our delivery technology applies

For Tβ4 the relevant delivery problem is local residence time, not oral absorption. A mucoadhesive, multi-layer particle in an ophthalmic or topical vehicle could hold the peptide at the ocular surface or wound bed and release it over hours while shielding it from tear and tissue proteases. That work belongs with a partner running a regulated clinical program. We do not formulate TB-500 for research-chemical sale.

Developing a local peptide therapy? Ask us about mucoadhesive delivery feasibility.