Thymosin alpha 1 is an immunomodulatory peptide studied in several clinical contexts. A large placebo-controlled sepsis trial did not find a clear reduction in 28-day mortality.

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Thymosin alpha-1 is a synthetic 28-amino-acid peptide that modulates T-cell function, acting on thymocytes by stimulating their differentiation or converting them to active T cells. Reviews describe it as behaving differently depending on the host's inflammatory state - restoring immune homeostasis rather than uniformly stimulating immunity.

After subcutaneous administration it is rapidly absorbed, reaching peak serum concentrations within two hours, with a half-life of approximately two hours; blood levels return to baseline within 24 hours.

This is one of the better-studied peptides here. Phase 3 hepatitis B trials across 195 patients reported HBV DNA clearance of 40.6% and 25.6% at 6 and 12 months against 9.4% in controls. In hepatitis C, monotherapy did not beat placebo, but combination with interferon alfa-2b reported 71% ALT normalisation against 35% for interferon alone. The largest and most rigorous trial is negative: TESTS (BMJ 2025), a multicentre double-blind placebo-controlled phase 3 trial in 1,106 adults with sepsis, found 28-day all-cause mortality of 23.4% on thymosin alpha-1 against 24.1% on placebo - no evidence of benefit. It is marketed as thymalfasin (Zadaxin) in a number of countries but is not FDA-approved.

Generally well tolerated; most studies observed only local injection-site irritation, and in the TESTS sepsis trial no safety outcome differed significantly from placebo. FDA removed thymosin alpha-1 from the Category 2 interim compounding list in September 2024 after the nomination was withdrawn, which is a procedural change rather than a safety finding.

Results are condition-specific and do not support general immune-enhancement claims. This record does not provide an indication, dose, or treatment recommendation.