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Synthetic 28-amino-acid thymic peptide (thymalfasin); immunomodulator

Thymosin Alpha-1

Approvedaka Thymalfasin, Zadaxin, Ta1, TA-1

Thymosin alpha-1 is one of the most clinically studied thymic peptides, used in a number of countries to modulate immune responses in viral hepatitis, as a vaccine adjuvant, and as adjunctive therapy in sepsis and some cancers. The evidence base is substantial but mixed: multiple randomized trials and meta-analyses exist, yet results are heterogeneous and it has not achieved approval by the FDA or the EMA. Where it is marketed it is a prescription medicine used under medical supervision.

Mechanism

In plain terms, thymosin alpha-1 helps adjust the immune system, shifting it toward a more effective antiviral and cell-mediated response. Technically, it is a synthetic copy of a naturally occurring thymic peptide (a 28-amino-acid fragment of prothymosin alpha) that is reported to act largely through Toll-like receptor signalling (notably TLR9 and TLR2) on dendritic cells and via effects on T-lymphocyte maturation. It is described as promoting T-helper-1 cytokine responses, enhancing dendritic-cell and natural-killer-cell function, and restoring lymphocyte counts in immunosuppressed states, which underlies its use as an immunomodulator rather than a direct antiviral or antibiotic.

Regulatory Status by Region

  • United States (FDA)Not FDA-approved for any indication; remains investigational in the United States despite approval in many other countries, and has been the subject of US clinical study and orphan-drug interest without a marketing approval.
  • China (NMPA) and other marketsApproved and marketed as thymalfasin (Zadaxin) in China and numerous other countries (reportedly more than 30) for chronic hepatitis B and C and as an immune-system adjuvant, with additional local uses such as adjunctive care in sepsis and some cancers. Prescription medicine where approved.
  • Australia (TGA)Not entered on the Australian Register of Therapeutic Goods (ARTG); no approved thymalfasin product in Australia.
  • European Union (EMA)No EMA centralized marketing authorisation; not authorised as a medicine at the EU level.
  • WADANot listed by name on the WADA Prohibited List; as an immunomodulatory peptide it is not currently a named prohibited substance, though athletes should verify current status with their anti-doping organisation.

Key Studies

  • The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial (Wu J, Zhou L, Liu J, et al. Crit Care. 2013;17(1):R8. PMID 23327199; DOI 10.1186/cc11932)
  • Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial (Chien RN, Liaw YF, Chen TC, Yeh CT, Sheen IS. Hepatology. 1998;27(5):1383-1387. PMID 9581695)