Synthetic 28-amino-acid thymic peptide (thymalfasin); immunomodulator
Thymosin Alpha-1
Unclearaka 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 (opens in a new tab) (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 (opens in a new tab) (Chien RN, Liaw YF, Chen TC, Yeh CT, Sheen IS. Hepatology. 1998;27(5):1383-1387. PMID 9581695)
Related Clinical Trials
- AI-assisted Subtyping-directed Precision Treatment in Acute Aortic DissectionN/A · Not Yet Recruiting
- Study of Adebrelimab Combined With Thymalfasin and Chemotherapy for Neoadjuvant Treatment of Esophageal CancerPhase 2 · Not Yet Recruiting
- Thymosin-α1 for Recurrent Implantation FailurePhase 2/Phase 3 · Recruiting
- A Study Evaluating Neoadjuvant Chemotherapy, Concurrent Chemoradiotherapy Combined With Dual Immune Checkpoint Blockade in Patients With Locally Advanced Non-Small Cell Lung CancerPhase 2 · Recruiting
- Phase II Trial of Neoadjuvant Thymalfasin, PD-1 Inhibitor, and Chemoradiotherapy for cStage III GEJ AdenocarcinomaPhase 2 · Recruiting
- A Study Evaluating Concurrent Chemoradiotherapy Combined With Dual Immune Checkpoint Blockade for Limited-stage Small Cell Lung CancerPhase 2 · Not Yet Recruiting
- Protective Effect of Ulinastatin and Thymosin α1 Against Negative Immune Dysregulation and Organ Dysfunction After Acute Aortic Dissection Surgery (PANDA XI)N/A · Enrolling By Invitation
- "Thymalfasin Immunotherapy Study with Triple Regimen in Advanced MSS/pMMR Colorectal Cancer"Phase 2 · Recruiting
Latest research
- Thymosin α-1 in Cancer Therapy: Immunomodulatory Mechanisms, Clinical Applications, and Translational Perspectives. (opens in a new tab)
European journal of pharmacology · Aug 25, 2026
Common Questions
- What is Thymosin Alpha-1?
- Thymosin alpha-1 (thymalfasin) is a synthetic 28-amino-acid immune-modulating peptide, originally isolated from the thymus and marketed as Zadaxin. It is approved in many countries (for example China and a number of other markets) for chronic hepatitis B and C and as an immune-system adjuvant, but it is not approved by the US FDA, is not centrally authorised by the EMA, and is not registered by Australia's TGA.
- Is Thymosin Alpha-1 approved for medical use?
- Thymosin Alpha-1 does not have a settled approval status and is not an approved medicine for general clinical use. 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. European Union (EMA): No EMA centralized marketing authorisation; not authorised as a medicine at the EU level. Australia (TGA): Not entered on the Australian Register of Therapeutic Goods (ARTG); no approved thymalfasin product in Australia.
- How does Thymosin Alpha-1 work?
- 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.
- Is Thymosin Alpha-1 legal in Australia?
- Thymosin Alpha-1 in Australia (TGA): Not entered on the Australian Register of Therapeutic Goods (ARTG); no approved thymalfasin product in Australia.
- Is Thymosin Alpha-1 banned in sport?
- Thymosin Alpha-1 under the World Anti-Doping Agency (WADA) code: Not 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.