Thymosin alpha-1
Also called Thymalfasin, Ta1, Tα1, Thymosin alpha-1 acetate
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In 30 seconds
A 28-amino-acid peptide first isolated from calf thymus; thymalfasin is the lab-made version.[1]
Tested in large trials; a 2025 sepsis trial of 1,106 adults found no clear effect on deaths.[3]
Not approved in the US, but reported as approved in a number of other countries.[1][7]
How far has the research gotten?
Sold as Zadaxin in some countries. FDA says it couldn't verify every claimed approval.[1]
People in its biggest studies
How many people each study enrolled, as reported.Research over time
Papers on PubMed each year that mention Thymosin alpha-1.15 papers in 2025FDA says it hasn't approved any product containing thymosin alpha-1.[1]
What studies used
What each paper reports. A record of published research, not a recommendation.28-day all-cause mortality versus placebo at 22 centres in China (NCT02867267). The abstract reports 23.4% vs 24.1% mortality (HR 0.99), with possible subgroup differences by age and diabetes.
BMJ (Clinical research ed.) · 2025 · PubMed 39814420What the paper reports
not stated in abstract (abstract describes subcutaneous injection every 12 hours for 7 days without giving the dose)
Who: Human (1106 adults with sepsis enrolled; 1089 analysed)28-day all-cause mortality, SOFA score and monocyte HLA-DR versus a control group at six hospitals in China (NCT00711620). The abstract reports 26.0% vs 35.0% mortality with a marginal P value.
Critical care (London, England) · 2013 · PubMed 23327199What the paper reports
not stated in abstract
Who: Human (361 ICU patients with severe sepsis)Whether adding Ta-1 to entecavir changed rates of liver decompensation, liver cancer or death compared with entecavir alone. The abstract reports no significant difference in these endpoints.
Expert opinion on biological therapy · 2018 · PubMed 30063860What the paper reports
not stated in abstract (52 weeks of Ta-1 plus entecavir after 26 weeks of entecavir)
Who: Human (690 patients with HBV-related compensated cirrhosis)FDA's list of bulk substances it says may raise significant safety risks if pharmacies compound them. Thymosin alpha-1 was on it until its nomination was withdrawn.[4]
What it is, in full 4
Thymosin alpha-1 is a 28-amino-acid peptide first isolated from calf thymus tissue in 1977; thymalfasin is the chemically made version, with the same amino acid sequence.[1]
It is described as an immune-modulating agent that is thought to work mainly by boosting T-cell function.[2]
In a 2025 phase 3 placebo-controlled trial of adults with sepsis in China, it did not clearly reduce deaths from any cause at 28 days.[3]
FDA has stated that it has approved no drug products containing thymosin alpha-1, although the product Zadaxin has been reported as approved in a number of other countries.[1][6][7]
Regulatory details 6
In its December 4, 2024 advisory committee presentation, FDA stated that it has approved no drug products containing Ta1, and that Ta1 is not approved in the United States, Japan, or Europe (except Italy). Drugs@FDA (openFDA) and DailyMed searches for 'thymalfasin' on 2026-10-06 also returned no matches.[1]
Checked 2026-10-06FDA's December 2024 presentation says Ta1 is not approved in Europe 'except Italy'. The product, indication and date of the Italian approval are not given.[1]
Checked 2026-10-06A 2009 review says thymosin alpha-1 is approved in more than 35 countries for hepatitis B and C and as an immune stimulant and adjuvant (source 7). A 2002 drug profile says SciClone marketed it as Zadaxin and lists approvals or launches including: Venezuela (January 1999, HBV and HCV); Sri Lanka and Brunei (August 1999); Thailand, Laos and Malta (March 2000, HBV); South Korea (April 2000, as an influenza vaccine adjuvant); India (February 2001, HBV); the Philippines (July 2001); expanded HBV/HCV approval in Mexico (July 2001); and launches in Argentina, China, Peru, the Philippines and Singapore (source 6). Separately, FDA, citing SciClone's 2014 annual report, says it could not independently verify the claimed approvals in every country named (source 1).[6]
Checked 2026-10-06FDA's category 2 page lists thymosin-alpha 1 (Ta1) in its table of substances previously in category 2 whose nominations were withdrawn. FDA's stated concerns: possible immunogenicity, peptide impurity and characterization issues, and safety information too limited to judge the extent of any safety issues. Page content current as of 04/22/2026.[4]
Checked 2026-10-06FDA evaluated Ta1 (free base) and Ta1 acetate on its own initiative after the nomination was withdrawn and recommended against adding them to the 503A Bulks List. At the December 4, 2024 Pharmacy Compounding Advisory Committee meeting, the votes on adding them were 4 yes and 17 no for each.[5]
Checked 2026-10-06Thymosin alpha-1 and thymalfasin do not appear by name in the 2026 Prohibited List, which names only thymosin-beta-4 and its derivatives (e.g., TB-500) under S2.3. This draft does not judge whether any general category would apply.[8]
Checked 2026-10-06Human trials on ClinicalTrials.gov
An intervention search of ClinicalTrials.gov for 'thymalfasin' on 2026-10-06 returned 64 records, including the completed phase 3 sepsis trial NCT02867267 and many phase 2 oncology studies, several of them listed as recruiting.[9]
All sources 13
- Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances - FDA presentation, Pharmacy Compounding Advisory Committee, December 4, 2024U.S. Food and Drug Administration
- Ancell CD et al. Thymosin alpha-1. Am J Health Syst Pharm 2001 (PMID 11381492)PubMed / NCBI
- Wu J et al. BMJ 2025, TESTS trial (PMID 39814420)PubMed / NCBI
- Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (category 2 page)U.S. Food and Drug Administration
- Final Summary Minutes, Pharmacy Compounding Advisory Committee, December 4, 2024U.S. Food and Drug Administration
- Billich A. Thymosin alpha1. SciClone Pharmaceuticals. Curr Opin Investig Drugs 2002 (PMID 12090542)PubMed / NCBI
- Goldstein AL. From lab to bedside: emerging clinical applications of thymosin alpha 1. Expert Opin Biol Ther 2009 (PMID 19392576)PubMed / NCBI
- WADA Prohibited List 2026World Anti-Doping Agency
- ClinicalTrials.gov API intervention search: thymalfasinClinicalTrials.gov / NLM
- Wu J et al. Crit Care 2013, ETASS trial (PMID 23327199)PubMed / NCBI
- Wu X et al. Expert Opin Biol Ther 2018 (PMID 30063860)PubMed / NCBI
- openFDA Drugs@FDA search: thymalfasin (no matches)U.S. Food and Drug Administration (openFDA)
- DailyMed SPL search: thymalfasin (0 results)DailyMed / NLM
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