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Thymosin alpha-1 protocol

Thymosin alpha-1 is a 28-amino-acid peptide first found in thymus extract. The lab-made version, thymalfasin (brand Zadaxin), is approved in some countries, mainly for hepatitis B. A large 2025 sepsis trial found no clear benefit.

Approved in more than 35 countries as thymalfasin (Zadaxin), for hepatitis B and C (per a 2020 review)Not approved as a medicine by the US FDASepsis: no clear benefit in a 1,106-person phase 3 trial
ProtocolMixingResultsSide effectsHow it worksSources

The protocol at a glance

In hepatitis B trials, thymosin alpha-1 was given as 1.6 mg under the skin twice a week for 26 weeks. In the sepsis trial it was 1.6 mg every 12 hours for up to 7 days.

Use studiedAmount and schedule
Chronic hepatitis B (trial, 98 people)1.6 mg under the skin twice a week for 26 weeks (a second group got 52 weeks)
Sepsis (phase 3 TESTS, 1,106 adults)1.6 mg under the skin every 12 hours for up to 7 days

Chien 1998 (Hepatology) and Wu 2025 (BMJ, NCT02867267). The BMJ paper calls 1.6 mg twice a week the conventional dose for cancers and viral hepatitis. Hepatitis B use dates from before today's antiviral drugs.

Community reports

Community and research-supplier sites commonly describe 1.6 mg under the skin twice a week for 4 to 8 weeks. These are user reports.

What people say they do, collected from community discussions. Not tested in a trial; shown so you can compare it with the evidence above.

Mixing calculator

Enter the vial size, the water you add and the amount you want to draw; it gives the mark on a 100-unit (1 mL) insulin syringe.

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What the trials found

Two trials. Hepatitis B: 98 people, 26-week course, measured 18 months after starting. Sepsis: 1,089 adults analysed, measured as deaths within 28 days.

40.6%hepatitis B complete virus response, 26-week course
9.4%same measure in the untreated group
23.4%died within 28 days, sepsis, thymosin alpha-1
24.1%died within 28 days, sepsis, placebo (no clear difference)

Chien RN et al. Hepatology 1998 (PMID 9581695); Wu J et al. BMJ 2025 (PMID 39814420, hazard ratio 0.99, 95% CI 0.77 to 1.27).

Side effects

  • No significant side effects were seen in the hepatitis B trial.
  • In the sepsis trial no safety outcome differed from placebo.
  • The sepsis trial hinted at different effects by age and diabetes. Those were subgroup findings, not firm results.

How it works

Immune modulation (lab data)

Lab studies show it can influence T-cell production and maturation, raise interferon-gamma and interleukin-2 signals, and activate natural killer cells.

Sources

  • Chien RN et al. Hepatology 1998, PMID 9581695
  • Wu J et al. BMJ 2025 (TESTS phase 3), PMID 39814420, NCT02867267
  • Dominari A et al. World J Virol 2020 (review: approved in more than 35 countries), PMID 33362999
  • Expert Rev Anti Infect Ther 2004 (thymalfasin for hepatitis B; Zadaxin, SciClone; 28 amino acids), PMID 15482167
  • Drugs@FDA / openFDA search: no thymalfasin product