PeptideFederation

Thymic immunomodulatory peptide

Thymosin Alpha-1

Also known as Thymalfasin, Zadaxin, Tα1

Approved medicine

Summary

Thymosin alpha-1 is a 28-amino-acid peptide from the thymus that modulates T-cell and dendritic-cell function. As thymalfasin, it is approved in several countries outside the US for chronic hepatitis B and as a vaccine or chemotherapy adjunct. Large trials in sepsis have not shown a mortality benefit.

Structure

  1. S1
  2. D2
  3. A3
  4. A4
  5. V5
  6. D6
  7. T7
  8. S8
  9. S9
  10. E10
  11. I11
  12. T12
  13. T13
  14. K14
  15. D15
  16. L16
  17. K17
  18. E18
  19. K19
  20. K20
  21. E21
  22. V22
  23. V23
  24. E24
  25. E25
  26. A26
  27. E27
  28. N28

HydrophobicGly / ProPolarBasic (+)Acidic (−)

N-terminally acetylated. Originally isolated from calf thymus; the synthetic drug is thymalfasin.

How it works

Tα1 acts on Toll-like receptors on dendritic cells and promotes T-cell maturation, Th1 cytokine production and natural killer cell activity. It is described as an immune modulator rather than a stimulant because it can also dampen excessive inflammation.

Research use cases

Areas where Thymosin Alpha-1 has been studied. Inclusion here does not mean it works for that purpose.

  • Chronic hepatitis B and C (approved outside the US)
  • Vaccine response in immunocompromised people
  • Sepsis and severe infection
  • Adjunct in cancer immunotherapy research

What the research found

Literature review

A comprehensive review summarizes decades of trials in hepatitis, cancer and infection, and notes that results vary widely in quality and that many trials were small or open-label.1

Severe COVID-19 (retrospective)

A retrospective study from China in 2020 reported lower mortality and restored T-cell counts in severe COVID-19 patients given Tα1. Retrospective designs cannot rule out confounding.2

Sepsis RCT

A multicentre randomized trial in China (the TESTS trial) found no significant reduction in 28-day all-cause mortality with thymosin alpha-1 versus placebo in adults with sepsis.3

Safety and open questions

Generally well tolerated in clinical trials; local injection-site reactions are the most common effect.

Regulatory status

Approved as thymalfasin (Zadaxin) in a number of countries outside the US, including China, for hepatitis B and as an immune adjunct. Not FDA-approved. Named in the February 2026 HHS compounding announcement.

Status was accurate when this page was last reviewed on October 26, 2026. Regulations change; check with the relevant authority before relying on it.

Thymosin Alpha-1: common questions

Is thymosin alpha-1 related to thymosin beta-4 (TB-500)?

Only by name. Both were isolated from thymus extracts, but they are unrelated proteins with different structures and functions.

Is Thymosin Alpha-1 approved for human use?

Approved as thymalfasin (Zadaxin) in a number of countries outside the US, including China, for hepatitis B and as an immune adjunct. Not FDA-approved. Named in the February 2026 HHS compounding announcement.

References

  1. Dominari A, Hathaway D, Pandav K, et al. (2020). Thymosin alpha 1: A comprehensive review of the literature. World Journal of Virology.
  2. Liu Y, Pan Y, Hu Z, et al. (2020). Thymosin Alpha 1 Reduces the Mortality of Severe Coronavirus Disease 2019 by Restoration of Lymphocytopenia and Reversion of Exhausted T Cells. Clinical Infectious Diseases.
  3. Wu J, Pei F, Zhou L, et al. (2025). The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ.

Links open a PubMed search for the exact title, or the original source where one is given.