What the studies show
Injection-site reactions; no signal for serious harm in TESTS or in long clinical use. Subgroup findings in TESTS (worse in under-60s, better in diabetics) are hypothesis-generating only.
Several well-run randomised trials in people, pointing the same way. You can plan around this. It still says nothing about whether the effect is worth the side effects for you.
- 1Liu F, et al. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial.BMJ, 2025; 388:e0825831,106 adults; 28-day mortality 23.4% vs 24.1%.
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 cause safety?
What studies are behind the grade?
Is Thymosin α1 approved for this?
Other outcomes for Thymosin α1
- ASepsis mortality1 large phase 3 RCT + earlier smaller RCTs
- BChronic hepatitis B (viral response)10+ RCTs, mostly small
- BVaccine response in the elderly and dialysis patientsSeveral RCTs
- CCOVID-19 outcomesObservational + small RCTs
Reviewed 3 September 2026. Grades count human evidence only; see how LYO grades. Not medical advice. Correct this page →