Compound research

Thymosin Alpha-1: Research Overview & Current Status

By the Best Peptide Stores Editorial TeamLast reviewed 2026-08-08 · Also known as: Ta1, Thymalfasin, Zadaxin

Approved (non-drug / other indication)

Thymosin Alpha-1 is a Thymic peptide / immunomodulator. Current research status: approved (non-drug / other indication). Thymalfasin (Zadaxin) is approved in more than 35 countries for chronic hepatitis B, hepatitis C, and as an immunomodulatory agent, but has not been approved by the FDA or EMA. In 2023 the FDA placed additional restrictions on its compounding status in the United States. Sepsis, despite extensive research, has never been an approved indication anywhere.

Overview

Thymosin alpha-1 is a 28-amino-acid peptide originally isolated from thymic tissue extract and later synthesized as thymalfasin, studied for its immune-modulating effects on T-cell function and cytokine signaling. It has an established international regulatory history distinct from most research peptides in this class.

Thymic peptide / immunomodulator

Research timeline

1970s-1980s
Thymosin alpha-1 isolated and characterized from thymic tissue extract; synthetic thymalfasin subsequently developed.
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1990s-2000s
Thymalfasin (Zadaxin) approved in 35+ countries for chronic hepatitis B and C and general immune modulation.
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2008-2010
ETASS trial (multicenter RCT, six Chinese tertiary hospitals) evaluated thymosin alpha-1 effects on 28-day mortality and immunofunction in severe sepsis.
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2016
Meta-analysis of 19 RCTs (530 patients across 10 mortality-reporting trials) reported a significant reduction in mortality with Ta1 (RR 0.59, 95% CI 0.45-0.77).
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2016-2020
TESTS trial — a multicenter, double-blind, placebo-controlled Phase 3 trial at 22 Chinese centers — found no significant overall mortality benefit from Ta1 in sepsis, with subgroup analyses suggesting differential age/comorbidity effects.
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2020
NCT04487444 registered evaluating thymalfasin (thymosin alpha-1) for treatment of COVID-19 infection.
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2023
FDA placed additional restrictions on thymosin alpha-1 compounding status in the United States.
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2025
Updated systematic review/meta-analysis of 11 RCTs (1,927 sepsis patients) reported a significant 28-day mortality reduction with Ta1 (OR 0.73, 95% CI 0.59-0.90), while cautioning that evidence reliability remains uncertain.
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Active & recent research

Phase 3, completed

TESTS trial

Definitive multicenter placebo-controlled evaluation of Ta1 for sepsis mortality; found no significant overall benefit but signaled possible age/comorbidity-dependent effects

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Registered clinical trial

Thymalfasin for COVID-19 infection

Evaluating immunomodulatory treatment effects of thymalfasin in COVID-19 patients

NCT04487444 on ClinicalTrials.gov →Source →

Systematic review, 11 RCTs, ~1,927 patients

2025 updated meta-analysis of sepsis RCTs

Re-evaluating 28-day mortality outcomes with Ta1 across the accumulated sepsis trial literature

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Key findings

A 2025 systematic review and meta-analysis of 11 RCTs (1,927 sepsis patients) reported a statistically significant 28-day mortality reduction associated with Ta1 administration (OR 0.73), while explicitly noting the reliability of the underlying evidence remains uncertain.
The largest and most rigorous trial to date, the placebo-controlled Phase 3 TESTS trial, found no significant overall mortality benefit in the full sepsis population, illustrating a divergence between meta-analytic pooled results and the single largest RCT.
TESTS trial subgroup analyses suggested a complex, age- and comorbidity-dependent effect pattern, with signals that Ta1 could potentially harm younger sepsis patients while possibly benefiting older patients and those with diabetes — described by researchers as requiring further confirmation.
Thymalfasin's clearest, most established evidence base remains its approved use (in 35+ countries outside the U.S./EU) for chronic hepatitis B and C, distinct from its investigational sepsis and COVID-19 research.

Safety & regulatory notes

Thymalfasin (Zadaxin) is approved in 35+ countries for hepatitis B/C and immune modulation but has no FDA or EMA approval; the FDA added compounding restrictions in 2023. Sepsis remains an investigational, off-label research area with mixed trial results — the largest placebo-controlled Phase 3 trial did not confirm an overall mortality benefit, despite earlier and more recent meta-analyses suggesting one.

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Where it's sold for research

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Thymosin Alpha-1 FAQ

Is thymosin alpha-1 FDA-approved?+

No. Thymalfasin (Zadaxin) is approved in more than 35 countries for chronic hepatitis B/C and immune modulation, but it has never received FDA or EMA approval, and in 2023 the FDA added compounding restrictions in the U.S.

Does thymosin alpha-1 reduce mortality in sepsis?+

The evidence is mixed. Earlier meta-analyses and a 2025 updated meta-analysis (11 RCTs) reported significant mortality reduction, but the largest, most rigorous placebo-controlled Phase 3 trial (TESTS) found no significant overall benefit, with subgroup effects suggesting the picture is more complex than pooled analyses imply.

Has thymosin alpha-1 been studied for COVID-19?+

Yes — a registered clinical trial (NCT04487444) evaluated thymalfasin as a treatment for COVID-19 infection, reflecting interest in its immunomodulatory properties during the pandemic era.

What is thymosin alpha-1's approved medical use?+

Its clearest approved use, under the brand Zadaxin, is for chronic hepatitis B and hepatitis C and as a general immunomodulatory agent, in jurisdictions outside the U.S. and EU.

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