Claimed effect · Thymosin α1

Does Thymosin α1 help with chronic hepatitis B?

B
Grade B — probable, not settled10+ RCTs, mostly small · effect size: small
Short answerProbable, not settled. Human data exist (10+ RCTs, mostly small) and mostly agree, showing a small effect — but too few, too small, or not yet peer-reviewed for a firm answer. Trials from the 1990s–2000s show modest increases in sustained response, alone or with interferon; heterogeneous quality. The basis for the Zadaxin approvals.

What the studies show

Trials from the 1990s–2000s show modest increases in sustained response, alone or with interferon; heterogeneous quality. The basis for the Zadaxin approvals.

Human trials exist and mostly agree, but there are too few of them, they are too small, or one big one is still reading out. Expect the grade to move.

  1. 1
    Thymalfasin (Zadaxin) clinical overview: hepatitis B and vaccine-adjuvant randomised trials.Multiple journals, 1996–2015Heterogeneous, mostly small RCTs.

In context

Thymosin α1 is a 28-amino-acid peptide from the thymus that nudges T-cells and dendritic cells toward a stronger antiviral response. It has been sold as Zadaxin for hepatitis B and as an immune adjunct in China, Italy and some thirty other countries since the 1990s, but the largest trial ever run on it — 1,106 adults with sepsis, published in the BMJ in January 2025 — found no reduction in 28-day mortality (23.4% versus 24.1%). It is not approved in the US, EU-wide or UK.

Thymosin α1 is approved outside us/eu (zadaxin). Legal status differs by country — see the regulation section or the jurisdiction pages.

Questions

Is Thymosin α1 proven to help with chronic hepatitis B?
Not yet settled. 10+ RCTs, mostly small — LYO grades it B, meaning probable but liable to change as trials read out.
What studies are behind the grade?
Trials from the 1990s–2000s show modest increases in sustained response, alone or with interferon; heterogeneous quality. The basis for the Zadaxin approvals.
Is Thymosin α1 approved for this?
Thymosin α1 is an approved medicine (Approved outside US/EU (Zadaxin)); whether this particular outcome is a licensed indication is stated on the compound page's regulation section.

Other outcomes for Thymosin α1

Reviewed 3 September 2026. Grades count human evidence only; see how LYO grades. Not medical advice. Correct this page →