Thymosin Alpha-1

Also known as: Tα1, thymalfasin, Zadaxin

Wellness

In plain English

Thymosin alpha-1 is a peptide that helps regulate the immune system. It is approved in some countries (as thymalfasin/Zadaxin) for hepatitis and as an immune booster, and it has been studied for serious infections. Results are mixed: an early trial in severe sepsis was encouraging, but a larger, more rigorous 2025 trial did not find a survival benefit. In the U.S. it is not an approved finished drug and is used off-label/compounded.

The science

Thymosin alpha-1 is a 28-amino-acid immunomodulatory peptide that enhances T-cell and dendritic-cell function, largely via Toll-like receptor signaling. In the ETASS trial (Wu et al., Critical Care 2013; n=361), adjunctive Tα1 in severe sepsis was associated with lower 28-day mortality (26.0% vs 35.0%) with borderline statistical significance and improved immune markers. However, the larger, double-blind, placebo-controlled phase 3 TESTS trial (2025; n=1,106) found no significant reduction in 28-day mortality, tempering enthusiasm. It is approved in several countries (thymalfasin) for chronic hepatitis B and as a vaccine adjuvant, but is not an FDA-approved finished product in the U.S. Human evidence is mixed and indication-dependent.

References

• Wu J et al., Crit Care 2013 (ETASS)
• Pei F et al., BMJ 2025 (TESTS; null for mortality)