TB-500

TB-500 is a synthetic, N-terminally acetylated heptapeptide (Ac-LKKTETQ) corresponding to the actin-binding region (residues 17–23) of thymosin beta-4, an endogenous G-actin-sequestering protein. The parent molecule binds monomeric G-actin (inhibiting its incorporation into filamentous actin) to regulate the actin cytoskeleton, and in preclinical models this activity is associated with promotion of cell migration, angiogenesis (linked to VEGF) and tissue repair.

Human evidence

Primarily animal and in-vitro studies of thymosin beta-4; no published human clinical trials of the TB-500 fragment itself.

Regulatory status

Not approved as a drug by the FDA or other major regulators for any indication; sold for research use only. In April 2026 the FDA removed TB-500 (along with 11 other peptides) from the interim 503A Category 2 bulk-substances list and scheduled it for FDA Pharmacy Compounding Advisory Committee (PCAC) review on July 23–24, 2026 for potential Category 1 (compoundable) status, with wound healing cited as the indication under consideration. Removal from Category 2 does not authorize compounding, and PCAC is advisory—a favorable vote is not itself FDA approval. Some jurisdictions (e.g., Australia—Schedule 4, effective June 2016—and New Zealand) classify thymosin beta-4/TB-500 as a prescription-only medicine for supply.

• —Studied in animal models for soft-tissue, tendon, ligament and muscle injury repair and wound healing.
• —Investigated for roles in cell migration and angiogenesis via actin-cytoskeleton regulation.
• —Examined in preclinical work on cardiac tissue repair and protection after ischaemic injury.
• —Researched for anti-inflammatory and tissue-regeneration effects attributed to thymosin beta-4 biology.

• ⚠No published human clinical trials of the TB-500 fragment, so its human safety profile is not established from controlled studies.
• ⚠Preclinical concern: in animal/in-vitro models thymosin beta-4 overexpression has been associated with increased tumour growth, cell migration and VEGF-mediated angiogenesis/metastasis (a JNCI 2003 mouse melanoma study reported a mean 46.7 vs 10.9 metastatic lung nodules, ~2.3-fold more cell migration and ~4.4-fold more tumour blood vessels), raising theoretical questions about effects on existing or undiagnosed cancers.
• ⚠Products sold as 'TB-500' vary in actual content (Ac-LKKTETQ fragment vs full-length thymosin beta-4); identity, purity and sterility of research material are not guaranteed, and the FDA's 2023 Category 2 rationale broadly cited immunogenicity, peptide-related impurity and insufficient-safety-data concerns for peptides in this group.
• ⚠Prohibited in sport at all times by WADA under Section S2 (peptide hormones, growth factors, related substances and mimetics).