Thymosin alpha-1 is a thymus-derived peptide that acts on immune cells. It has been studied for hepatitis B, infections and cancer. Most of the human trials come from China and other Asian countries. This article covers the trials we could check against two sources.
What it is
Thymosin alpha-1 is a peptide originally isolated from the thymus. Guidelines describe it as an immune modulator, and it has been used mainly in Asia.
Its human evidence is uneven. Some trials are small, single-centre and older, which limits what they can show.
The sepsis trial, TESTS
TESTS was a multicentre, double-blind, placebo-controlled phase 3 trial in 22 centres in China, run from September 2016 to December 2020. It randomised 1,106 adults with sepsis 1:1 to thymosin alpha-1 or placebo. Injections were given under the skin every 12 hours for seven days, unless the person left intensive care, died or withdrew.
What the trial measured
- Primary outcome: all-cause death within 28 days of randomisation.
- Analysed: 1,089 people (542 on thymosin alpha-1, 547 on placebo).
- Deaths: 127 (23.4%) on thymosin alpha-1 and 132 (24.1%) on placebo, not a significant difference.
- No secondary or safety outcome differed significantly between the groups.
Subgroups
The authors pre-specified subgroup analyses. Under 60 years, the hazard ratio was 1.67 (1.04 to 2.67). At 60 and over it was 0.81 (0.61 to 1.09). In people with diabetes it was 0.58 (0.35 to 0.99), and without diabetes 1.16 (0.87 to 1.53). The authors describe these as a potential differential effect, not as confirmed benefits.
Other trials and meta-analyses
A 2025 meta-analysis of sepsis trials pooled 11 randomised trials. It reported a pooled reduction in 28-day mortality, but the subgroup of higher-quality trials and the multicentre subgroup did not show a clear benefit. Its authors state that the sample size is still too small for a firm answer, and that the TESTS trial may change the picture.
Approval outside the US
The 2015 Asian-Pacific hepatitis B guideline reports that thymosin alpha-1 has been licensed in some Asian countries. We did not check current regulator records, so this article gives no count of approvals and makes no claim about approval in the US.
What this does not say
- It does not show that thymosin alpha-1 lowers death in sepsis. The main result was negative.
- It does not show benefit for immunity, longevity, infection prevention or general wellness in healthy adults.
- The subgroup results are exploratory and were not tested as the main outcome.
- A small open-label pilot in COVID-19 (Shehadeh et al., 2023) was described by its authors as preliminary.
- Country approvals are not evidence of benefit for a given person.
How we use this
Our physicians read this evidence before recommending anything. The largest trial did not show a mortality benefit, so we do not use thymosin alpha-1 on the strength of it for sepsis, immunity or longevity.
Where a physician does consider it, the dose and schedule come from the trials that were run, not from wellness schedules.
Explore weight loss treatmentsSources
- 1.Wu J, Pei F, Zhou L, 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
- 2.Gu B, Zhou Y, Nie Y, et al. Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Cellular and Infection Microbiology, 2025
- 3.Sarin SK, Kumar M, Lau GK, et al. Asian-Pacific clinical practice guidelines on the management of hepatitis B: a 2015 update. Hepatology International, 2016
- 4.Shehadeh F, Benitez G, Mylona EK, et al. A pilot trial of thymalfasin (thymosin-α-1) to treat hospitalized patients with hypoxemia and lymphocytopenia due to COVID-19 infection. Journal of Infectious Diseases, 2023