Thymosin Beta-4

What it is

TB-500 is a synthetic peptide corresponding to an actin-binding region of the naturally occurring protein thymosin beta-4 (Tβ4), commonly described as a ~17-amino-acid fragment. In marketing, "TB-500" and "thymosin beta-4" are often used interchangeably, but they are not identical entities — a distinction that matters when reading claims about the research behind it.S3

Marketed as

TB-500 is marketed as a "recovery" and "healing" peptide — for injury repair, flexibility, and endurance — and is often sold stacked with BPC-157. These are marketing claims, not established effects.S3

Regulatory status (US)

TB-500 is not an FDA-approved drug for any human indication.S1S3 On FDA's compounding framework it appears in the "nominated but withdrawn" portion of Category 2 — bulk substances that "may present significant safety risks".S1 It is on the July 23, 2026 PCAC agenda for possible inclusion on the 503A Bulks List; the use FDA evaluated is wound healing (public docket FDA-2025-N-6895). Advisory-committee recommendations are non-binding, and any listing would follow an FDA decision and rulemaking.S2

Around the world

TB-500 is not approved for human use anywhere — no regulator (FDA, EMA, MHRA, TGA) has established its safety or efficacy.S3 It is also prohibited in animal sport, reflecting its circulation in veterinary / equine settings as an unapproved substance.S3

Evidence

Human evidence for injectable TB-500 is very limited: there are no completed, published Phase 2/3 trials of the systemic fragment for musculoskeletal indications. Full-length Tβ4 has been studied on a separate regulatory track (for example, an ophthalmic candidate), which is distinct from the TB-500 fragment sold for "recovery".S3

Anti-doping

TB-500 is prohibited at all times on the WADA Prohibited List under S2 (peptide hormones, growth factors, related substances and mimetics), and has been listed for years.S3

Safety

FDA's general Category 2 concerns apply: possible immunogenicity for certain routes of administration, complexity in peptide-related impurities and active-ingredient characterization, and only limited human safety information.S1

What's changing

The July 23, 2026 PCAC discussion is the near-term event to watch: a recommendation plus subsequent FDA action would be what actually changes TB-500's compounding status — not the meeting alone.S2