Claimed effect · Thymosin α1

Does Thymosin α1 help with sepsis mortality?

A
Grade A — established in humans1 large phase 3 RCT + earlier smaller RCTs · effect size: not measurable
Short answerEstablished in humans. 1 large phase 3 RCT + earlier smaller RCTs point the same way: no measurable effect, or none yet shown. TESTS, 1,106 adults in 22 Chinese ICUs, twice-daily injections for 7 days: 28-day mortality 23.4% versus 24.1% on placebo (hazard ratio 0.99, 95% CI 0.77–1.27). No secondary or safety outcome differed. Earlier smaller trials that suggested benefit are superseded.

What the studies show

TESTS, 1,106 adults in 22 Chinese ICUs, twice-daily injections for 7 days: 28-day mortality 23.4% versus 24.1% on placebo (hazard ratio 0.99, 95% CI 0.77–1.27). No secondary or safety outcome differed. Earlier smaller trials that suggested benefit are superseded.

“28 day all cause mortality occurred in 127 participants (23.4%) in the thymosin α1 group and 132 (24.1%) in the placebo group (hazard ratio 0.99, 95% confidence interval 0.77 to 1.27; P=0.93 with log-rank test).”

Verbatim, from the abstractWu J, et al. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ, 2025; 388:e082583

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.

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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 sepsis mortality?
Yes, as far as human trials can show it: 1 large phase 3 RCT + earlier smaller RCTs. LYO grades this outcome A.
What studies are behind the grade?
TESTS, 1,106 adults in 22 Chinese ICUs, twice-daily injections for 7 days: 28-day mortality 23.4% versus 24.1% on placebo (hazard ratio 0.99, 95% CI 0.77–1.27). No secondary or safety outcome differed. Earlier smaller trials that suggested benefit are superseded.
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

Written and maintained by LYO Research — how pages are written and checked. Reviewed 3 September 2026. Grades count human evidence only; see how LYO grades. Not medical advice. Correct this page →