Thymosin Alpha-1 (Zadaxin) — Immune Modulator Peptide — Peptides
Thymic peptide approved in 30+ countries for hepatitis B and as immune adjuvant. Not FDA-approved in the US.
Overview
Thymosin alpha-1 (Ta1, Zadaxin) is a 28-amino-acid peptide originally isolated from thymic tissue (Thymosin Fraction 5) by Allan Goldstein at George Washington University in the 1970s. It is a key regulator of immune function, enhancing both innate and adaptive immunity through dendritic cell maturation, T-cell differentiation, and natural killer cell activation. Thymosin alpha-1 is approved in over 35 countries (including China, Italy, Singapore, Philippines, and multiple Latin American nations) for treatment of chronic hepatitis B and C, as an immune adjuvant in vaccination of immunocompromised patients, and as supportive therapy in various cancers. Despite extensive clinical trial data — including over 40 clinical trials — thymosin alpha-1 has not received FDA approval in the United States. In hepatitis B, thymosin alpha-1 at 1.6 mg subcutaneously twice weekly for 6 months produced sustained viral response rates comparable to interferon-alpha but with significantly fewer side effects. During the COVID-19 pandemic, thymosin alpha-1 gained attention for its potential to restore T-cell function in severe cases, with several Chinese clinical studies showing reduced mortality in critically ill patients. The compound is available from compounding pharmacies in the US and is used in functional and integrative medicine for immune optimization.
Indications
- Approved (35+ countries): Chronic hepatitis B treatment
- Approved (some countries): Hepatitis C adjunct therapy
- Approved (some countries): Immune adjuvant for vaccines in immunocompromised
- Off-label: Immune system optimization and chronic infection support
- Investigational: Cancer immunotherapy adjunct
- Investigational: COVID-19 immune modulation
Mechanism of Action
Thymosin alpha-1 promotes maturation of dendritic cells through TLR9-mediated signaling, enhancing antigen presentation to T cells
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Thymosin Alpha-1 (Zadaxin) | 1.6 mg | Twice weekly | Standard clinical dose for hepatitis B (approved in 35+ countries) |
| Thymosin Alpha-1 | 1.6 mg | Once daily x 5 days, then twice weekly | Intensive immune support protocol |
Evidence Grade
GRADE B
Safety & Contraindications
- Excellent safety profile in clinical trials — well-tolerated
- Injection site reactions (mild erythema, pain) most common
- Rarely: low-grade fever, fatigue (immune activation)
- Theoretical risk of autoimmune flare in predisposed individuals
- Not FDA-approved in US despite extensive international data
- Compounding pharmacy quality may vary in the US