Considering thymalfasin therapy
Research notes
The short answer: the Food and Drug Administration (FDA), the agency overseeing US drugs, could not tell from the studies whether thymosin alpha-1 helped with any of the health problems reviewed. The biggest trial in sepsis, a severe reaction to infection, did not clearly show fewer deaths.
A result from a study of hospital patients cannot tell us whether a treatment helps healthy people. Ask who took part, what treatment the comparison group received and what changed.
Government review
In 2024, the Food and Drug Administration (FDA) reviewed thymosin alpha-1 for 12 uses. These included liver infections, COVID, cancers and sepsis, a severe reaction to infection. It also reviewed adding the medicine to flu vaccination for people with weak body defences.
For every use, the studies left the FDA unsure whether it helped people. That does not prove the substance can never help.
Open the FDA reviewHospital trial
Sepsis is a dangerous body-wide reaction to an infection. The TESTS trial, published in 2025, enrolled 1,106 adults with sepsis in hospitals in China.
At 28 days, deaths were 23.4% in the thymosin alpha-1 group and 24.1% in the placebo group. A placebo is a dummy treatment used for comparison.
The small difference did not show clearly that the medicine reduced deaths. This study of hospital patients cannot tell us whether it helps healthy people.
The study named SciClone Pharmaceuticals, the maker of thymalfasin (Zadaxin), as a supporter. Some authors also received grants or fees from the company.
Read the TESTS paper recordThe source record available to this guide does not say what kind of support the company gave the study. It cannot tell us whether that help was money, medicine or something else.
Review of trials
A 2025 review brought together results from 11 trials of sepsis treatment. It reported fewer deaths when it counted all the trials. The authors then looked only at trials they rated as higher quality. In that smaller group, they could no longer be sure the medicine reduced deaths. They also found no clear reduction when looking only at trials held at several hospitals.
Some researchers who worked on TESTS also wrote this review. The two reports therefore share some researchers, rather than giving checks by wholly separate teams.
Read the review of sepsis trialsThe source record does not explain how the review rated trial quality. Sharing researchers does not by itself tell us that a result is right or wrong. Ask how the review checked each trial and why some were left out.