What the studies show
Chinese observational cohorts and small randomised studies reported lower mortality in severe COVID-19; confounded and never confirmed in a large trial.
A few small or poorly-controlled human studies. Enough to be interesting; not enough to count on. Most of what gets called “clinically proven” online lives here.
- 1Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials.Front Cell Infect Microbiol, 2025Includes TESTS; earlier pooled estimates were driven by small trials.
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 COVID-19 outcomes?
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
- ASafetyadverseTESTS + decades of use
Reviewed 3 September 2026. Grades count human evidence only; see how LYO grades. Not medical advice. Correct this page →