Thymosin Alpha-1

Thymosin alpha 1 · Thymosin alpha1 · Thymalfasin · Zadaxin

Snapshot

Indications	Contraindications
Sepsis adjunct¹ Chronic hepatitis B² Acute-on-chronic liver failure^{3, 4} Non-small cell lung cancer with chemo⁵ Gastric cancer with chemotherapy⁶ Radiation pneumonitis⁷	Hypersensitivity to thymosin alpha 1⁸ Deliberate immunosuppression⁸

Thymosin alpha-1 (thymalfasin) is a synthetic thymic peptide that enhances T-cell responses, which is the basis for its use as an immune-supporting injectable⁹. The United States (US) Food and Drug Administration (FDA) previously listed it among compounding substances with significant safety risks, citing immunogenicity, and the nominations were later withdrawn¹⁰. It is used as an adjunct in sepsis, chronic hepatitis B, and chemotherapy-treated lung cancer, and in coronavirus disease 2019 (COVID-19), mostly in hospitalized or immunocompromised patients. An Indonesian label approves it for chronic hepatitis B⁸.

Sepsis meta-analyses report lower mortality, with low-quality underlying trials^{1, 11}. A Cochrane review in chronic hepatitis B rates the certainty of evidence as very low, and a COVID-19 meta-analysis found lower mortality in moderate to critical disease while calling for randomized trials. In 2026, a single-arm phase 2 trial added thymalfasin to immune checkpoint inhibitor chemotherapy before surgery in locally advanced gastric cancer and reported encouraging pathological response; no randomized trial has confirmed it¹². Seven products list thymosin alpha-1 in the US supplement label database; Zadaxin is the marketed injectable abroad.

An FDA advisory committee briefing found a lack of evidence of effectiveness across these uses and raised concern about use after stem cell transplantation¹³. Per the Indonesian label, caution applies when combining it with other immune-modulating medications⁸.

Last updated October 17, 2026. Read how we make monographs.

In the full monograph

53 sources, 39 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources