A synthetic fragment of Thymosin Beta-4, a 43-amino-acid protein involved in cell migration, wound healing, and anti-inflammation. Widely used in veterinary and research settings for tissue repair.
TB-500 is a synthetic version of Thymosin Beta-4 (Tβ4), a naturally occurring 43-amino-acid protein found in nearly all human and animal cells. Tβ4 is one of the most abundant intracellular peptides and plays a critical role in cell motility, wound healing, and anti-inflammatory signaling.
Unlike BPC-157 (which promotes healing primarily through angiogenesis), TB-500 works by sequestering G-actin — the monomeric form of actin — which promotes cell migration, blood vessel formation, and tissue remodeling. It has been most extensively studied in equine (horse racing) veterinary medicine and is commonly stacked with BPC-157 for complementary healing effects.
TB-500 has a long history in veterinary medicine, particularly in equine sports where it has been used to treat tendon, ligament, and muscle injuries in racehorses. This veterinary track record — while not a substitute for human clinical trials — provides a substantial body of observational evidence for its healing properties. In human medicine, TB-500 is most commonly used by functional medicine practitioners and sports medicine clinicians for musculoskeletal injuries, often in combination with BPC-157.
The regulatory landscape for TB-500 shifted significantly in 2026. Like BPC-157, TB-500 (as Thymosin Beta-4) was placed on the FDA's Category 2 restricted list in late 2023. The February 2026 HHS announcement indicated that TB-500 is among the approximately 14 peptides expected to return to Category 1 status, restoring eligibility for compounding by licensed pharmacies. WADA has banned TB-500 since 2010 under category S0 (non-approved substances), meaning athletes cannot use it regardless of therapeutic intent. For the full regulatory timeline, see our March 2026 briefing.
TB-500 is rich in charged residues (Lys, Glu, Asp), making it highly hydrophilic and water-soluble. The key functional motif is the actin-binding domain LKKTETQ (residues 17-23), which is essential for G-actin interaction. The N-terminal tetrapeptide AcSDKP has independent anti-fibrotic activity.
TB-500's primary mechanism is actin cytoskeleton regulation. Actin is the most abundant protein in eukaryotic cells and is essential for cell movement, division, and structural integrity. By controlling the G-actin/F-actin balance, TB-500 directly influences how quickly cells can migrate to damaged tissue.
| Pathway | Effect | Significance |
|---|---|---|
| G-actin sequestration | Binds monomeric actin to prevent premature polymerization | Ensures actin availability for cell migration when needed |
| AcSDKP release | The N-terminal tetrapeptide AcSDKP is anti-fibrotic | Reduces scar tissue formation and promotes functional tissue regeneration |
| Laminin/integrin upregulation | Increases cell surface adhesion receptors | Enhances cell attachment to extracellular matrix at injury sites |
| Anti-inflammatory | Reduces IL-1β, TNF-α, and other inflammatory cytokines | Creates an environment conducive to healing rather than chronic inflammation |
TB-500's preclinical evidence spans cardiac, dermal, neurological, and musculoskeletal applications.
| Study Area | Design | Key Findings | Evidence |
|---|---|---|---|
| Cardiac repair | Mouse MI model | Reduced infarct size, improved ejection fraction, promoted cardiomyocyte survival post-heart attack | Preclinical |
| Wound healing | Rat/mouse dermal wounds | Accelerated wound closure, increased angiogenesis and collagen deposition | Preclinical |
| Corneal healing | Rat corneal injury | Accelerated epithelial migration and wound closure | Preclinical (Phase II human attempted) |
| Equine tendon | Horse tendon injuries | Widely used in horse racing; improved tendon healing and return to performance | Veterinary clinical |
| Neurological | Rat TBI/stroke models | Promoted neuronal survival and functional recovery; stimulated oligodendrocyte differentiation | Preclinical |
Limited human safety data: Most TB-500 safety information comes from veterinary use and in vitro studies. No Phase II or Phase III human clinical trials have been completed. The preclinical safety profile is favorable — no organ toxicity or mutagenicity has been reported at standard doses — but the absence of formal human safety studies means the risk profile is not fully characterized.
Cancer concerns: Thymosin Beta-4 is upregulated in certain cancer cell lines, raising theoretical concerns about whether exogenous TB-500 could promote tumor growth or metastasis. However, there is no clinical evidence that TB-500 administration causes or accelerates cancer. Some researchers have noted that Tβ4's role in cancer cells may be a consequence of tumor biology (rapidly dividing cells need more actin regulation) rather than a causative factor. Nevertheless, most clinicians recommend against use in patients with active malignancies.
Injection site reactions: Mild redness and swelling at subcutaneous injection sites have been reported. TB-500 is typically administered at 2-5 mg twice weekly during an initial loading phase, then reduced to a maintenance dose of 2 mg once or twice weekly.
Quality and sourcing: As with all non-approved peptides, product quality from grey-market vendors varies significantly. The return to Category 1 compounding status will enable access through licensed pharmacies using pharmaceutical-grade API — a substantially safer sourcing pathway.
| Jurisdiction | Status |
|---|---|
| FDA | Not approved for any indication |
| WADA | Banned under S0 (non-approved substances) |
| Veterinary | Widely used in equine medicine (not FDA-approved for animals) |
| Feature | TB-500 | BPC-157 |
|---|---|---|
| Size | 43 amino acids (4,963 Da) | 15 amino acids (1,419 Da) |
| Origin | Thymus gland (Thymosin β4) | Human gastric juice protein |
| Primary mechanism | G-actin sequestration → cell migration | VEGFR2-Akt-eNOS → angiogenesis |
| Key action | Promotes cell migration to injury site | Builds new blood vessels to injured tissue |
| Oral bioavailability | No (injection only) | Yes (stable in gastric juice) |
| Best for | Systemic inflammation, muscle, cardiac | Tendons, gut, localized injuries |
| Combined use | Commonly stacked — complementary mechanisms (angiogenesis + cell migration) |