thymosin α-1

updated

Thymosin α-1 (thymalfasin, Zadaxin) is a 28-amino-acid peptide registered in China for specific chronic hepatitis B and vaccine-response uses, with no FDA approval found. It is used off label for general immune support and promoted for long COVID and as a cancer adjunct. In TESTS, the largest sepsis trial, 28-day mortality was 23.4% against 24.1% on placebo among 1,089 patients, and no controlled study shows broad immune benefit in healthy people. Graded B for disease-specific human research and use outside the US; sepsis and general wellness are not on its label.

N-terminally acetylated 28-amino-acid peptide

  • 28-amino-acid acetylated peptide
  • Also called thymalfasin
  • Authorization and labeled indications vary by country

Where and for what is thymalfasin currently authorized?

China's national pharmaceutical data center lists Zadaxin thymalfasin for injection, 1.6 mg, under registration 国药准字HJ20171177 through May 5, 2027. The Chinese instruction names compensated chronic hepatitis B and vaccine-response enhancement in immunocompromised people. Sepsis and general wellness are not named indications. No exact-name FDA approval appears in the cited US records.

A current Chinese product record supports those named uses. The claim of approval in about 35 countries remains unverified across individual regulators.

source: China product record · Zadaxin 1.6 mg, National Center for Medical Information, China, record published December 5, 2023

source: Zadaxin Chinese instruction · indications and safety, Chinese medical-use instruction reproduced by DXY, modified October 26, 2020

source: Thymalfasin status · US and China records, Drugs@FDA, openFDA, and Chinese drug-registration records.

Did thymosin α-1 reduce deaths in the TESTS phase 3 trial?

TESTS found no mortality benefit. Among 1,089 participants in the modified intention-to-treat analysis, 28-day mortality was 23.4% with thymosin α-1 and 24.1% with placebo, hazard ratio 0.97 with a 95% confidence interval from 0.76 to 1.24 and P=0.82. Secondary and safety outcomes also did not differ significantly.

TESTS randomized 1,106 adults at 22 centers in China from 2016 to 2020 and tested subcutaneous injections every 12 hours for seven days. The trial was registered on ClinicalTrials.gov as NCT02867267.

Age and diabetes subgroup interactions were prespecified but remain exploratory in a trial with a null primary outcome and multiple subgroup tests.

source: TESTS · null 28-day mortality, Wu et al., BMJ, 2025

What did the earlier ETASS sepsis trial report?

ETASS reported 28-day mortality in 47 of 181 thymosin α-1 patients, 26.0%, versus 63 of 180 placebo patients, 35.0%. The unstratified relative risk was 0.74 with a 95% confidence interval from 0.54 to 1.02 and P=0.062; a log-rank analysis gave P=0.049.

The six-center China study used centralized, center-stratified block randomization and saline placebo. Participants and outcome analysts were masked. Hospital mortality was 28.7% versus 39.4%, but the primary 28-day comparison was sensitive to analysis method and the later, larger TESTS trial did not reproduce a mortality benefit.

The full report was published in English and registered as NCT00711620. No matching ChiCTR result record appears in the cited public record, so the available trial records are ClinicalTrials.gov and the full publication.

source: ETASS · earlier mortality signal, Wu et al., Critical Care, 2013

source: TESTS · null 28-day mortality

Did older hepatitis B trials establish a durable treatment benefit?

A 97-person phase 3 trial reported complete response in 14% with thymosin α-1 versus 4% with placebo, but the difference did not reach conventional statistical significance at P=0.084. These studies predate today's oral antiviral standards and do not establish an advantage over current therapy.

Biochemical, viral, and serologic response definitions also differ from the outcomes and comparators used in modern hepatitis B care.

source: Thymalfasin HBV · older phase 3, Mutchnick et al., Hepatology, 1999

Is there controlled evidence for general immune support in healthy people?

The cited disease-specific trials do not establish a broad benefit in healthy people. Sepsis, chronic hepatitis, cancer adjuncts, and immunodeficiency are different populations with different endpoints; none can be converted into a universal immune-support claim.

Changes in immune markers do not automatically improve infections, symptoms, hospitalization, or survival.

source: TESTS · null 28-day mortality

source: Thymalfasin HBV · older phase 3

What can the trial record say about thymosin α-1 side effects and safety?

The Chinese instruction lists injection-site pain as generally mild and uncommon and also names rare redness, transient muscle atrophy, joint pain with swelling, and rash. It contraindicates hypersensitivity and advises against intentional immunosuppression, such as after organ transplant, unless benefit clearly outweighs risk.

The label says interactions have not been adequately assessed, pregnancy use requires a clear need, and pediatric safety and efficacy are not established. Chronic hepatitis B treatment can produce ALT flares, so liver tests need label-directed monitoring.

In TESTS, adverse events occurred in 66.4% with thymosin α-1 and 67.6% with placebo; serious adverse events occurred in 26.8% and 29.3%. Seven days in critically ill adults cannot define chronic or cross-product safety.

source: Zadaxin Chinese instruction · indications and safety

source: TESTS · null 28-day mortality

Which product name belongs to the evidence?

Thymosin α-1 is the endogenous-peptide name, while thymalfasin is the pharmaceutical name used for the acetylated 28-amino-acid drug substance. Product salt, formulation, manufacturer, and route still matter when applying a trial or label. Thymosin α-1 and TB-500 are different molecules. Thymosin α-1 is a 28-amino-acid peptide, while the key ingredient of TB-500 is acetylated LKKTETQ, a seven-residue active site of thymosin beta-4, a separate 43-amino-acid protein.

source: Thymalfasin HBV · older phase 3

source: Thymosin α-1 · 28 amino acids, Li J, Liu CH, Wang FS. Peptides. 2010;31(11):2151-8. PMID 20699109.

source: TB-500 · acetylated LKKTETQ, Ho EN et al. J Chromatogr A. 2012;1265:57-69. PMID 23084823.

source: Thymosin β4 · 43 amino acids, Kozaczuk A, Selmi A, Bednarek R. Protein Expr Purif. 2013;90(2):142-52. PMID 23769831.

Studies and sources

TESTS · null 28-day mortality

Randomized trial

Wu et al., BMJ, 2025

In 1,089 analyzed adults, 28-day mortality was 23.4% with thymosin α-1 and 24.1% with placebo, hazard ratio 0.97, 95% CI 0.76 to 1.24, P=0.82; no secondary or safety outcome differed significantly.

Participants / model
Adults with Sepsis-3 sepsis at 22 centers in China
Treatment
Subcutaneous thymosin α-1 or placebo every 12 hours for seven days
Follow-up
28-day primary follow-up
Study design
Multicenter, double-blind, randomized, placebo-controlled phase 3 trial

Subgroup signals do not override the null primary outcome.

Read the original source
ETASS · earlier mortality signal

Randomized trial

Wu et al., Critical Care, 2013

28-day mortality was 47 of 181 with thymosin α-1 versus 63 of 180 with placebo; RR 0.74, 95% CI 0.54 to 1.02, P=0.062, while log-rank P=0.049.

Participants / model
361 followed adults with severe sepsis at six centers in China
Treatment
Zadaxin 1.6 mg subcutaneously twice daily for five days then daily for two days versus saline placebo, with standard care
Follow-up
28-day primary follow-up
Study design
Centralized, center-stratified, block-randomized, participant-masked, saline-placebo-controlled trial

The trial was conducted in China and its full report is in English. Significance depended on analysis method, and TESTS later found no benefit.

Read the original source
Thymalfasin HBV · older phase 3

Randomized trial

Mutchnick et al., Hepatology, 1999

The 97-person trial reported complete response in 14% versus 4% with placebo, with P=0.084.

Participants / model
Adults with chronic hepatitis B in an older treatment era
Treatment
Thymosin α-1 or placebo
Follow-up
Six months treatment and follow-up
Study design
Randomized, double-blind, placebo-controlled phase 3 trial

The trial was small, not conventionally significant, and predates current oral antiviral standards.

Read the original source
China product record · Zadaxin 1.6 mg

Chinese national pharmaceutical data record

National Center for Medical Information, China, record published December 5, 2023

Lists Zadaxin thymalfasin for injection 1.6 mg under 国药准字HJ20171177, issued May 6, 2022 and valid through May 5, 2027.

Participants / model
Chinese imported-drug registration
Treatment
Zadaxin thymalfasin for injection, 1.6 mg
Follow-up
Registration valid through May 5, 2027
Study design
Chinese national pharmaceutical product database record

This verifies one current national product record; it does not verify a global country count or add indications beyond the product instruction.

Read the original source
Zadaxin Chinese instruction · indications and safety

Chinese label reproduction

Chinese medical-use instruction reproduced by DXY, modified October 26, 2020

Names compensated chronic hepatitis B and vaccine-response enhancement in immunocompromised patients, with product dosing, contraindications, and adverse effects.

  • Chronic hepatitis B: 1.6 mg subcutaneously twice weekly for six months.
  • Vaccine-response enhancement: 1.6 mg subcutaneously twice weekly for four weeks, starting with vaccination.
  • The instruction does not name sepsis or general immune support.
Participants / model
Adults covered by the reproduced Chinese Zadaxin instruction
Treatment
Thymalfasin 1.6 mg subcutaneous injection
Follow-up
Instruction reproduction modified October 26, 2020
Study design
Chinese-language product-instruction reproduction

The indication and guidance wording comes from a 2020 instruction reproduction; the national database record separately supports current product registration.

Read the original source
Thymosin α-1 · 28 amino acids

Narrative review

Li J, Liu CH, Wang FS. Peptides. 2010;31(11):2151-8. PMID 20699109.

Thymosin alpha 1 is a 28-amino acid peptide, first described and characterized from calf thymuses in 1977.

Read the original source
TB-500 · acetylated LKKTETQ

Analytical identity or detection study

Ho EN et al. J Chromatogr A. 2012;1265:57-69. PMID 23084823.

TB-500 contains a synthetic version of LKKTETQ, the segment at positions 17 to 23 of thymosin β4; its key ingredient is LKKTETQ with an acetylated N-terminus.

Read the original source
Thymosin β4 · 43 amino acids

Cell study

Kozaczuk A, Selmi A, Bednarek R. Protein Expr Purif. 2013;90(2):142-52. PMID 23769831.

Thymosin β4 is an actin-binding peptide of 43 amino acids involved in tissue regeneration and angiogenesis.

Read the original source

Why is thymosin α-1 in B tier?

B reflects disease-specific human research and non-US regulatory use. The largest Chinese sepsis trial was negative, and the Chinese label does not include sepsis or general wellness use.

how tiers are graded: methodology · every cited source · about reptides.

Research reference, not medical advice. Entries distinguish product labels, study doses and reported protocols. Check the linked source for the product, route and population.