Thymosin Alpha-1

Thymalfasin · Zadaxin

Immunomodulating thymic peptide approved in 30+ countries for hepatitis B/C and as a vaccine adjuvant.

Approved outside USGut & Immune

Not FDA-approved. Approved in China, Italy and many other countries. Not FDA-approved. This page describes research and public discussion; it is not a recommendation to use.

Overview

Thymalfasin is a 28-amino-acid peptide originally isolated from thymus tissue. It is approved outside the US for chronic hepatitis B and as an immune enhancer. It received orphan designations in the US but no approval.

Mechanism of action

Enhances T-cell maturation and function, dendritic-cell activity, and Toll-like receptor signaling.

Benefits & evidence ratings

Adjunct therapy for chronic hepatitis B (approved abroad)B Human clinical data

Possible mortality benefit in sepsis (TESTS trial: not significant)B Human clinical data

General immune boostD Anecdotal / community

Dosing

Doses show what has been studied or discussed — not guidance. Always follow your prescriber.

Source	Dose	Frequency	Duration	Route
Zadaxin labeling (hepatitis B) B Human clinical data	1.6 mg	Twice weekly	6 months	Subcutaneous

Clinical trials & studies

RCT2025
Thymosin α1 in sepsis — TESTS trial (BMJ)
1,106 patients; 28-day mortality not significantly reduced.

Safety

Side effects

Injection-site discomfort
Generally well tolerated

Contraindications

Organ transplant recipients on immunosuppression
Pregnancy

Interactions

Immunosuppressants (opposing effect)

Long-term safety

Favorable safety record over decades of use abroad.

Regulatory status

Approved outside US

Approved in China, Italy and many other countries. Not FDA-approved.