TB-500
Also known as: TB500, Thymosin Beta-4 Fragment, Tβ4 fragment, TB4 fragment
A synthetic peptide marketed for tendon, muscle, and soft-tissue healing, based on an actin-binding fragment of the natural protein Thymosin beta-4. Sold as a research chemical with essentially no controlled human evidence.
Not approved by the FDA for any use and sold for laboratory research only. It is often conflated with Thymosin beta-4 itself, but TB-500 is a distinct synthetic fragment. Injectable peptides of this type have been targeted by FDA enforcement and were not accepted for pharmacy compounding under section 503A.
What it is
TB-500 is a synthetic peptide sold as a research chemical for tissue healing and recovery. It is derived from — and frequently marketed as if it were — Thymosin beta-4 (Tβ4), a naturally occurring 43-amino-acid protein involved in actin binding, cell migration, and wound repair. In practice, TB-500 is a distinct, shorter synthetic fragment, and the two names should not be treated as interchangeable.
What it’s approved or studied for
Nothing. TB-500 is not approved by the FDA for any use and is sold for laboratory research only. The healing claims made for it — tendons, ligaments, muscle, connective tissue — are extrapolated largely from animal studies of the parent protein and related fragments, not from trials of TB-500 in people.
What human evidence exists
Effectively none of the controlled kind. As of this review, no published randomized controlled trial has tested injected TB-500 for any musculoskeletal or systemic indication in humans. The supporting record is Grade D preclinical evidence: rodent injury models, cell-migration assays, and mechanistic work on actin sequestration. That work is genuinely interesting, but it does not establish that TB-500 works or is safe in people. Long-term human safety is Grade U: unknown. (Note that the more studied relative, Thymosin beta-4, does have some human trial data for specific indications — see its own profile — but those trials used the full protein in defined formulations, not research-chemical TB-500.)
The major unknowns
Human pharmacokinetics, effective dose, and whether any rodent benefit translates to humans are all open. Because TB-500 promotes angiogenesis and cell migration in preclinical models, there is a theoretical, unquantified concern about effects on tumor growth. Product purity is a further problem: research-chemical supply is unregulated, so the identity and content of any given vial is uncertain.
Most important safety considerations
Because there is no controlled human safety data, the honest answer to “is it safe?” is that no one knows. Product quality is uncontrolled, it is prohibited in sport at all times under WADA’s S2 category, and it is not a legal therapeutic. This page summarizes the research record; it is not medical advice or an endorsement of use.
Evidence by outcome
Each outcome is graded on its own evidence — a compound can be strong for one use and unproven for another. See how we grade.
Signal in animal models; not demonstrated in humans. — Rodent injury models associated with the parent protein and related fragments report improved tissue architecture and reduced scar formation, but no controlled human trial has tested injected TB-500 for tendinopathy or ligament injury.
Preclinical only. — Animal muscle-crush and strain models show faster functional recovery; there is no human confirmation.
Animal and cell data only. — Actin-binding fragments promote keratinocyte and endothelial cell migration in vitro and in rodent wound models; human effectiveness is unestablished.
Preclinical signal, no human trials of TB-500.
Unknown — no controlled human safety data exist.
Safety
Common adverse effects
- Not established in humans; injection-site reactions reported anecdotally
Serious risks
- Unknown — no controlled human safety data; theoretical concern that pro-angiogenic activity could affect tumor growth; unregulated product quality and contamination risk
Contraindications
- No human contraindication data; not approved for human use
References