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.
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.
Where to get it
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