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Thymosin Alpha-1: quick citable summary
Thymosin Alpha-1 is listed by PeptaHub as a immune peptide with a research only legal-status classification. The page summarizes mechanism, research context, common routes, safety notes, and references for writers and AI answer engines.
PeptaHub. “Thymosin Alpha-1: Mechanism, Research Context, Safety.” peptahub.com, 2026. https://peptahub.com/peptides/thymosin-alpha-1. Licensed CC BY 4.0.
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What is Thymosin Alpha-1?
Thymosin Alpha-1 is a 28-amino-acid immune-modulating peptide (Zadaxin) acting via TLR9 and TLR2 to drive Th1 and regulatory T-cell responses. Marketed outside the US for hepatitis B and C, it is not FDA-approved and cannot legally be compounded here. Its controlled trial results are mixed.
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.
Reported study ranges
| Purpose | Route | Reported range | 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. |
Reported ranges are for research context only. Consult a qualified healthcare professional before using any peptide.
Convert Thymosin Alpha-1 research-range units
Need to convert mg to mcg, dose volume, or U-100 syringe units? The Thymosin Alpha-1 dose calculator is preloaded with these ranges, or use the general dose unit converter.
Research summary
Marketed as Zadaxin in a number of countries outside the US for chronic hepatitis B and as an adjunct in hepatitis C. The controlled evidence is mixed rather than settled. A randomized pilot in 67 HBeAg-positive chronic hepatitis B patients found higher HBeAg seroconversion with thymosin alpha-1 plus lamivudine at 24 weeks (26.5 versus 6.1 percent) but no significant difference at 52 weeks (Lee, J Gastroenterol Hepatol 2008). In severe sepsis, the 361-patient ETASS trial found 28-day mortality of 26.0 percent with Tα1 versus 35.0 percent in controls, which did not reach significance on the prespecified analysis (P=0.062), though a 2016 systematic review of 19 randomized trials pooled a mortality benefit while rating the evidence low quality. In COVID-19, a retrospective review of 76 severe cases in Wuhan reported lower mortality with Tα1 (11.1 versus 30.0 percent). It is not FDA-approved and cannot legally be compounded in the US.[1][2][3][4][5][6][7]
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 cannot legally be compounded in the US today. It was placed on the FDA's Category 2 bulk drug substances list in 2023, which put it outside enforcement discretion for compounding. It was not among the 12 peptides the FDA removed from Category 2 on April 15, 2026, so it remains in Category 2, and it was not among the seven substances heard by the Pharmacy Compounding Advisory Committee on July 23-24, 2026 nor the five scheduled for review before the end of February 2027. HHS Secretary Kennedy's February 2026 podcast remarks floated a broader set of substances than the action that followed, and Thymosin Alpha-1 was not covered by it. This entry previously stated that the compounding ban was lifted as of April 23, 2026; that was incorrect and was corrected on 2026-07-23. Thymosin Alpha-1 is approved under the brand name Zadaxin in more than 30 countries but is not FDA-approved in the US. Verify current federal and state rules before relying on access claims.
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 substances list in 2023 and was not among the 12 peptides the FDA removed from Category 2 on April 15, 2026, so it remains in Category 2 and cannot legally be compounded. No Pharmacy Compounding Advisory Committee review of Thymosin Alpha-1 has been scheduled.
It is marketed outside the US for chronic hepatitis B and as an adjunct in hepatitis C. Controlled data in hepatitis B are mixed: a randomized pilot found better HBeAg seroconversion at 24 weeks when added to lamivudine, but no significant difference at 52 weeks. It has also been studied in sepsis, where the largest randomized trial narrowly missed statistical significance, and in severe COVID-19, where the published evidence is retrospective.
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 reported as generally well-tolerated in the published trials. Reported side effects are mild and include injection site discomfort, transient flu-like symptoms, and fatigue. The 361-patient severe sepsis trial recorded no serious drug-related adverse events. Long-term safety outside the studied indications and durations is not characterized.
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 TreatmentReview
- The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trialPubMed
- Combination therapy of thymosin alpha-1 and lamivudine for HBeAg positive chronic hepatitis B: a prospective randomized, comparative pilot studyPubMed