28-amino acid acetylated peptide · Tα1 · Zadaxin
A 28-amino acid peptide first isolated from bovine thymus in 1972. Approved as a drug (Zadaxin, SciClone) in over 35 countries for hepatitis B, hepatitis C, and immunosuppressed patients. One of the most clinically documented immunomodulatory peptides in existence, with four decades of evidence from RCTs, real-world clinical use, and COVID-19 protocols. Remains a research compound in the US.
01, Research Summary
Thymosin Alpha-1 has one of the most substantial clinical evidence bases of any peptide in the immune category, a distinction that sets it apart from most research peptides where human trial data is sparse. Approved in over 35 countries under the brand name Zadaxin (SciClone), it has been used in clinical settings for decades for hepatitis B, hepatitis C, and as an immune adjunct in immunocompromised patients.
Clinical approval in 35+ countries based on RCT data. Thymosin Alpha-1 received regulatory approval across Asia, Eastern Europe, and Latin America on the basis of Phase 2 and 3 randomised controlled trials in hepatitis B and C, demonstrating immune restoration and virological response improvements.
Reduced 28-day mortality in critically ill COVID-19 patients. An observational study of 76 critically ill patients reported reduced mortality in the Thymosin Alpha-1-treated group, attributed to restoration of lymphocytopenia and reversal of T-cell exhaustion, both hallmarks of severe COVID-19 immune dysregulation.
Mixed results in non-severe patients. A larger retrospective study of 1,388 non-severe COVID-19 patients showed less clear benefit in the non-severe population, suggesting Thymosin Alpha-1's immune restoration effects are most meaningful in cases of significant immune dysfunction rather than mild disease.
The evidence is strongest for viral infection contexts where immune dysregulation is documented, hepatitis, severe infection, and immunocompromised states. Evidence for general longevity use goes beyond what the trials support. The US has not approved it for any indication despite the international evidence base.
02, Mechanism of Action
Thymosin Alpha-1 is a biological response modifier, it modulates the immune system toward appropriate function rather than simply stimulating or suppressing it. This bidirectional regulation is what makes it interesting for both infection and longevity contexts.
Tα1 promotes the differentiation and maturation of T-cells in the thymus and periphery. It specifically reverses T-cell exhaustion, the state of functional impairment that occurs in chronic viral infection, cancer, and aging, restoring immune surveillance capacity.
Tα1 activates Toll-like receptors (TLR-7, TLR-9) on distinct dendritic cell subsets, enhancing innate immune recognition of pathogens and improving antigen presentation to T-cells. This bridges innate and adaptive immunity, the mechanism behind its antiviral properties.
Uniquely, Tα1 modulates cytokine production in both directions depending on immune context: it increases pro-inflammatory cytokines when the immune system is suppressed (infections) and reduces them when over-activated (autoimmunity, cytokine storm). This context-dependent regulation is the basis of its "immune normalising" reputation.
Tα1 activates NK cells (natural killer cells, the innate immune system's primary cancer and viral surveillance mechanism) while expanding regulatory T-cells that prevent autoimmune overreaction. This dual effect supports immune vigilance without triggering inflammatory dysregulation.
03, Dosing Context
Clinical protocols from the approved countries and from the COVID-19 literature provide the clearest reference points for Thymosin Alpha-1 dosing.
| Protocol | Dose | Frequency | Duration | Context |
|---|---|---|---|---|
| Infection / acute | 1.6 mg | Twice weekly | 6–12 months | Based on hepatitis trial protocols |
| Longevity / immune maintenance | 1–1.6 mg | 1–2x weekly | 3–6 months, then reassess | Community protocol, limited trial basis |
| COVID-19 (observational) | 1.6 mg | Daily or twice daily | 7–14 days | Critically ill, Chinese clinical practice |
The 1.6 mg dose is the most clinically established, drawn directly from the hepatitis trial protocols and approved country labelling. Longevity use at lower frequencies is a community extrapolation from the infection data rather than a protocol derived from dedicated trials.
04, Community
Thymosin Alpha-1 is discussed in two distinct community contexts. In the longevity and biohacker community, it appears in immune optimisation protocols, often alongside other peptides as part of a comprehensive anti-aging stack. In the post-COVID community, it has attracted specific attention for long COVID immune dysregulation, where its T-cell exhaustion reversal mechanism aligns with documented post-viral immune abnormalities.
The community is notably more measured about Tα1 than about many other peptides, the international approval history and RCT evidence base seem to reduce the hype-to-evidence gap that characterises discussion of compounds with weaker data. Users tend to reference the hepatitis trial data and clinical use in approved countries as a baseline, rather than extrapolating broadly from mechanistic plausibility.