Quick summary
Thymosin Alpha-1 is a 28-amino-acid immune-modulating peptide (sold as Zadaxin) that acts via TLR9 and TLR2 to drive Th1 and regulatory T-cell responses. It is approved in over 35 countries for hepatitis B and C, is not FDA-approved, and is under FDA compounding review.
Overview
Thymosin Alpha-1 (Tα1) is a 28-amino-acid peptide originally isolated from thymic tissue and now produced synthetically. Sold as Zadaxin, it is approved in over 35 countries for treatment of hepatitis B, hepatitis C, and as an immune adjuvant in cancer therapy. It is a leading immune-modulating peptide used in integrative medicine.
Mechanism of action
Thymosin Alpha-1 modulates innate and adaptive immunity primarily through toll-like receptor (TLR) engagement. It acts as a potent agonist at TLR9 on dendritic cells and TLR2 on macrophages, triggering MyD88-dependent signaling that upregulates type I interferons (IFN-α/β), IL-12, and TNF-α. This drives differentiation of naive T-cells toward Th1 and regulatory T-cell (Treg) phenotypes, enhancing cytotoxic CD8+ T-cell responses against infected or malignant cells while suppressing excessive inflammatory cytokine production. Tα1 also promotes natural killer (NK) cell activation and augments dendritic cell antigen-presenting capacity. The dual pro-immune and immune-regulating activity explains its utility in both immunodeficiency states and autoimmune-adjacent conditions where immune dysregulation is present.
Dosing protocols
| Purpose | Route | Dosage | Frequency | Notes |
|---|---|---|---|---|
| immune support / chronic infection | subcutaneous | 1–2 mg | twice weekly | Standard induction protocol: 1.6 mg subcutaneously twice weekly for 4 weeks, then once weekly for maintenance. Zadaxin trials used 6–12 month courses. |
| oncology adjuvant support | subcutaneous | 3–3 mg | twice weekly | Higher dose (3.2 mg twice weekly) used in oncology applications to support immune reconstitution during chemotherapy. Typically administered alongside standard treatment. |
Dosing information is for educational purposes only. Consult a qualified healthcare professional before using any peptide.
Research summary
Approved in over 35 countries for chronic hepatitis B (proven to increase sustained virologic response rates) and hepatitis C (adjunctive). Phase 2 and 3 data exist for non-small cell lung cancer, sepsis, and COVID-19 (Italian hospitals reported mortality benefit in severe COVID-19 patients). A 2021 meta-analysis confirmed immune restoration in patients with solid tumors receiving chemotherapy. No FDA approval in the US; FDA is reviewing a citizen petition for compounding reinstatement as of 2024.[1][2][3][4][5]
Evidence grading
Each claimed benefit is graded by the strength of available evidence. Grades reflect study quality, not effect size.
Strong = multiple RCTs · Moderate = limited trials or observational · Preliminary = animal or in vitro only · Insufficient = anecdotal or no published data
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
Common stacks
Peptides commonly paired with Thymosin Alpha-1 for synergistic effects.
Legal status
Thymosin Alpha-1 was placed on the FDA Category 2 bulk drug substance list in 2023 (compounding ban). It is approved under the brand name Zadaxin in 35+ countries. As of February 2026, it is among the 14 peptides expected to be returned to compounding-eligible status per HHS Secretary Kennedy's announcement, though formal FDA publication of the updated list was still pending as of April 2026.
Sourcing & access
Research compound
Thymosin Alpha-1 is classified as a research compound. Regulatory status varies by jurisdiction. Always verify current legal status and source from vendors providing third-party certificates of analysis (COA).
Frequently asked questions
Thymosin Alpha-1 (Tα1) is a 28-amino-acid peptide originally isolated from thymic tissue and now produced synthetically. It is sold under the brand name Zadaxin and is used primarily as an immune modulator.
Tα1 acts as an agonist at TLR9 on dendritic cells and TLR2 on macrophages, triggering MyD88-dependent signaling that upregulates type I interferons, IL-12, and TNF-α. This drives differentiation of naive T-cells toward Th1 and regulatory T-cell phenotypes, enhancing cytotoxic CD8+ responses while suppressing excessive inflammatory cytokine production.
No. Thymosin Alpha-1 is approved in more than 35 countries under the brand name Zadaxin, but it is not FDA-approved in the United States. It was placed on the FDA Category 2 bulk drug substance list in 2023, and as of February 2026 it is among the 14 peptides expected to be returned to compounding-eligible status pending formal FDA publication.
It is approved internationally for treatment of chronic hepatitis B (with demonstrated increases in sustained virologic response rates) and adjunctive hepatitis C treatment. Phase 2 and 3 data also exist for non-small cell lung cancer, sepsis, and severe COVID-19.
A standard induction protocol is 1.6 mg subcutaneously twice weekly for 4 weeks, followed by once-weekly maintenance. Oncology applications use a higher dose of approximately 3.2 mg twice weekly to support immune reconstitution during chemotherapy.
Thymosin Alpha-1 has a plasma half-life of approximately 2 hours, with peak serum levels reached 1 to 2 hours after subcutaneous injection. Despite the short plasma exposure, immunomodulatory effects persist for days because the peptide drives durable downstream changes in T-cell differentiation, dendritic cell activation, and TLR-mediated gene expression, supporting twice-weekly dosing in standard protocols.
Thymosin Alpha-1 is generally well-tolerated across the clinical trial program that underpins its approval in over 35 countries. Reported side effects are mild and include injection site discomfort, transient flu-like symptoms consistent with cytokine activation, and fatigue. Serious adverse events are rare and no significant long-term safety signals have been identified during hepatitis B, hepatitis C, or oncology use.
Research references
- Thymosin Alpha 1 Reduces the Mortality of Severe Coronavirus Disease 2019 by Restoration of Lymphocytopenia and Reversion of Exhausted T CellsPubMed
- Comprehensive Review of the Safety and Efficacy of Thymosin Alpha 1 in Human Clinical TrialsPubMed
- The Efficacy of Thymosin Alpha 1 as Immunomodulatory Treatment for Sepsis: A Systematic Review of Randomized Controlled TrialsPubMed
- Thymosin Alpha 1 Is Associated with Improved Cellular Immunity and Reduced Infection Rate in Severe Acute Pancreatitis Patients in a Double-Blind Randomized Control StudyPubMed
- Immune Modulation with Thymosin Alpha 1 TreatmentPubMed