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Peptide Database

Immune research

Thymosin Alpha 1 (Ta1): Research, Mechanism & Current Evidence

Synthetic thymic hormone approved in a number of countries as an immune modulator, with a large trial record.

Also known as Tα1 · thymalfasin · Zadaxin · Ta1

Research use onlyStrongest evidence: controlled clinical trialReviewed
DatabaseReferences

What is Thymosin Alpha 1?

Thymosin alpha-1 is a synthetic peptide of 28 amino acids identical to a hormone produced by the thymus gland. It is marketed as Zadaxin and generically as thymalfasin.

It is approved in a number of countries — though not the UK or US — chiefly for hepatitis B and C and as an adjunct in immune-compromised patients.

Status: Approved in a number of countries. Not approved in the UK, US or EU.

What is Thymosin Alpha 1 researched for?

Chronic hepatitis B and C, where it has been studied both alone and alongside interferon.

Sepsis and severe infection, and immune function in older adults.

Use as a vaccine adjuvant in populations that respond poorly to vaccination.

  • FDA orphan designation for DiGeorge syndrome; restores T-cell function.
  • Improved antibody responses in elderly and hemodialysis patients (H1N1, COVID-19).
  • Restores CD4+ counts and reduces opportunistic infections.
  • Reduces pro-inflammatory cytokines TNF-α, IL-1β, IL-6 by 40-60%.
  • Enhanced antiviral efficacy when combined with interferon.
  • Helps manage inflammatory autoimmune conditions.
  • Restores immune function after surgical stress.
  • Manages immune suppression from intense training.
  • Supports thymus gland function with aging.
  • Delays age-related immune decline in elderly populations.

How does Thymosin Alpha 1 work?

Rather than stimulating the immune system indiscriminately, thymosin alpha-1 is described as modulating it: helping immature T cells mature and shifting the balance of immune signalling.

Mechanistically it has been reported to act through Toll-like receptors on dendritic cells, which are the cells that present targets to the rest of the immune system.

What does the research show?

It has one of the larger trial records of any compound in this database, with thousands of participants across studies and a consistently low rate of serious adverse events.

Results in hepatitis have been positive but modest, and studies in sepsis have produced mixed findings.

Limitations of the current evidence

Trial quality varies considerably, and several of the larger studies were conducted in settings where standard of care differs from current UK practice.

It has not been approved by the MHRA, FDA or EMA despite its approval elsewhere.

References

  1. Thymosin Alpha 1 Reduces the Mortality of Severe Coronavirus Disease 2019 by Restoration of Lymphocytopenia and Reversion of Exhausted T Cells

    Liu Y, Pan Y, Hu Z, et al. · Clinical infectious diseases : an official publication of the Infectious Diseases Society of America · 2020

    Mortality significantly reduced in severe COVID-19: 11.11% with thymosin alpha 1 vs 30.00% untreated (P=0.044). Restored CD4+ and CD8+ T-cell numbers and reversed T-cell exhaustion markers PD-1 and Tim-3.

    PMID 32442287

  2. The Efficacy and Safety of Thymosin Alpha 1 for Sepsis (TESTS): Multicentre, Double-Blinded, Randomised, Placebo-Controlled, Phase 3 Trial

    Liu J, Li J, He L, et al. · BMJ · 2025

    1,106 adults with sepsis across 22 centres. 28-day mortality: 23.4% thymosin alpha 1 vs 24.1% placebo (HR 0.99, P=0.93). No overall benefit, but prespecified subgroup analysis showed potential benefit in elderly and diabetic patients.

    Controlled clinical trial

  3. Thymosin Alpha 1: A Historical Overview Garaci E Annals of the New York Academy of

    Sciences · 2007

    Comprehensive overview of thymosin alpha 1 from discovery to clinical application. Evidence for combined treatments with interferon or IL-2 restoring immune responses depressed by tumor growth and/or cytostatic drugs.

  4. Comprehensive Review of the Safety and Efficacy of Thymosin Alpha 1 in Human Clinical Trials

    Dinetz E, Lee E · Alternative therapies in health and medicine · 2024

    Narrative review of 11,000+ patients across 30+ clinical trials. Exceptional safety profile with <1% serious adverse events. Applications in COVID-19, autoimmune conditions, hepatitis, and cancer.

    Review or meta-analysis · PMID 38308608

  5. This information is for educational and research purposes only. Consult a healthcare professional before use.

  6. A comprehensive research database for peptides, therapies, and protocols. Information provided for educational purposes only.

  7. © 2026 Peptide Database. For educational and research purposes only.

  8. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial

    Wu J, Pei F, Zhou L, et al. · BMJ (Clinical research ed.) · 2025

    Controlled clinical trial · PMID 39814420

  9. Thymosin alpha1: a historical overview

    Garaci E · Annals of the New York Academy of Sciences · 2007

    PMID 17567941

Common questions

Does Thymosin Alpha-1 actually work for COVID-19 or just reduce symptoms?

A clinical trial showed Thymosin Alpha-1 significantly reduced mortality in severe COVID-19 (11.11% vs 30% untreated, P=0.044) by restoring CD4+ and CD8+ T-cell numbers and reversing T-cell exhaustion. It works by immune restoration rather than direct antiviral activity.

Why is Thymosin Alpha-1 less popular than other immune peptides if it's studied so extensively?

Despite 11,000+ patients in 30+ trials with excellent safety (<1% serious adverse events), Thymosin Alpha-1 has limited commercial availability. It's not FDA-approved for most indications (only orphan status for DiGeorge syndrome), making prescription access difficult outside research settings or specific countries.