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Thymosin α1
Immune Modulator

Thymosin α1

Zadaxin

Thymosin alpha-1 (Tα1, thymalfasin) corresponds to the first 28 amino acids of prothymosin α and was first isolated from thymic extracts; it is also generated naturally in mammalian tissues by cleavage of prothymosin α. It was originally identified as the compound that restores immune function in thymectomized animals. SciClone Pharmaceuticals developed synthetic Tα1 (Zadaxin) outside the US and Europe and has obtained approvals in more than 30 countries; reviews describe its approved uses as chronic hepatitis B and C and as an immune stimulant and adjuvant. The standard regimen in hepatitis trials is 1.6 mg injected subcutaneously twice a week. In a 62-patient randomized study in HBeAg-positive chronic hepatitis B, a 6-month course was well tolerated and produced complete responses in 31% at the end of treatment and 48% six months later. A meta-analysis of four small randomized trials found that its benefit over interferon alpha was not significant at the end of therapy but emerged during follow-up. A 2026 Cochrane review of 10 trials (1,349 participants) found it may reduce mortality and serious adverse events in chronic hepatitis B, but judged the evidence low to very low certainty. In a 1,106-patient phase 3 trial in sepsis, Tα1 did not reduce 28-day mortality. Tα1 is not FDA-approved; in the US it is a research-only compound.

Specifications

Origin / ManufacturerSynthetic
Form FactorLyophilized vial

Clinical Evidence

Chronic hepatitis B: in a 62-patient randomized trial, 1.6 mg twice weekly for 6 months gave complete response in 31% at end of treatment and 48% at 6-month follow-up, with no side effects reported.

Clinical report reference

Chronic hepatitis B meta-analysis (4 RCTs, 199 patients): versus interferon alpha, no significant advantage at end of therapy, but higher virological, biochemical and complete response at 6 months post-treatment.

Clinical report reference

Cochrane review 2026 (10 RCTs, 1,349 participants): may reduce all-cause mortality and serious adverse events in chronic hepatitis B, but certainty of evidence is low to very low.

Clinical report reference

Sepsis (TESTS phase 3, 1,106 adults): no reduction in 28-day all-cause mortality versus placebo (23.4% vs 24.1%).

Clinical report reference

Frequently Asked Questions

Sources & References

Every clinical claim on this page traces to a primary peer-reviewed source.

  1. 1Ancell CD, Phipps J, Young L. Thymosin alpha-1. American journal of health-system pharmacy : AJHP : official journal of the American Society of Health-System Pharmacists. 2001;58(10):879-85; quiz 886-8. doi:10.1093/ajhp/58.10.886 PMID:11381492
  2. 2Sarandeses CS, Covelo G, Díaz-Jullien C, et al.. Prothymosin alpha is processed to thymosin alpha 1 and thymosin alpha 11 by a lysosomal asparaginyl endopeptidase. The Journal of biological chemistry. 2003;278(15):13286-93. doi:10.1074/jbc.M213005200 PMID:12554742
  3. 3Romani L, Bistoni F, Gaziano R, et al.. Thymosin alpha 1 activates dendritic cells for antifungal Th1 resistance through toll-like receptor signaling. Blood. 2004;103(11):4232-9. doi:10.1182/blood-2003-11-4036 PMID:14982877
  4. 4Sjogren MH. Thymalfasin: an immune system enhancer for the treatment of liver disease. Journal of gastroenterology and hepatology. 2004;19 Suppl 6:S69-72. doi:10.1111/j.1440-1746.2004.03635.x PMID:15546253
  5. 5Romani L, Bistoni F, Perruccio K, et al.. Thymosin alpha1 activates dendritic cell tryptophan catabolism and establishes a regulatory environment for balance of inflammation and tolerance. Blood. 2006;108(7):2265-74. doi:10.1182/blood-2006-02-004762 PMID:16741252
  6. 6You J, Zhuang L, Cheng HY, et al.. Efficacy of thymosin alpha-1 and interferon alpha in treatment of chronic viral hepatitis B: a randomized controlled study. World journal of gastroenterology. 2006;12(41):6715-21. doi:10.3748/wjg.v12.i41.6715 PMID:17075991
  7. 7Tuthill C. Issues in pharmaceutical development of thymosin alpha1 from preclinical studies through marketing. Annals of the New York Academy of Sciences. 2007;1112:351-6. doi:10.1196/annals.1415.007 PMID:17947591
  8. 8Yang YF, Zhao W, Zhong YD, et al.. Comparison of the efficacy of thymosin alpha-1 and interferon alpha in the treatment of chronic hepatitis B: a meta-analysis. Antiviral research. 2008;77(2):136-41. doi:10.1016/j.antiviral.2007.10.014 PMID:18078676
  9. 9Goldstein AL, Goldstein AL. From lab to bedside: emerging clinical applications of thymosin alpha 1. Expert opinion on biological therapy. 2009;9(5):593-608. doi:10.1517/14712590902911412 PMID:19392576
  10. 10King R, Tuthill C. Immune Modulation with Thymosin Alpha 1 Treatment. Vitamins and hormones. 2016;102:151-78. doi:10.1016/bs.vh.2016.04.003 PMID:27450734
  11. 11Wu J, Pei F, Zhou L, et al.. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ (Clinical research ed.). 2025;388:e082583. doi:10.1136/bmj-2024-082583 PMID:39814420
  12. 12Naing C, Ni H, Aung HH, et al.. Thymosin-ɑ1 for people with chronic hepatitis B. The Cochrane database of systematic reviews. 2026;9(9):CD014610. doi:10.1002/14651858.CD014610.pub2 PMID:42713852
  13. 13U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. FDA Human Drug Compounding. 2026.

Reviewed by

Clinical Research Review Board

Pharmacology & Endocrinology Review

All clinical claims cross-checked against primary sources. Read our editorial policy →

Reviewed by Clinical Research Review BoardPharmacology & Endocrinology Review

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