Thymosin Alpha-1: clinical evidence record
Also known as: Thymalfasin, Ta1, Zadaxin
Oliver Mackman · Editorial director · Best Business Loans Ltd (16833937)
Last updated 2026-07-19
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AI-friendly summary · Thymosin Alpha-1
Unusually for a research-tier peptide, thymosin alpha-1 has a genuine randomised human trial record. It is a licensed medicine (Zadaxin, thymalfasin) in a number of countries including China and Italy, principally for chronic hepatitis B, but it holds no marketing authorisation in the United Kingdom. Published work includes a large randomised study in metastatic melanoma, randomised work in HBV-related cirrhosis, systematic reviews and meta-analyses in COVID-19 and severe acute pancreatitis, and a multicentre phase 3 placebo-controlled trial in sepsis published in the BMJ in 2025. The state of the evidence is best described as substantial but not settled: the phase 3 sepsis trial did not establish a mortality benefit, several of the meta-analyses rest on small trials of mixed quality and are heavily weighted to Chinese cohorts, and the indications studied are hospital critical-care and infectious-disease settings rather than wellness, recovery or longevity use. There is no controlled human evidence supporting the uses for which it is marketed to consumers. Because the compound modulates immune function, the theoretical risk area is anyone immunosuppressed, immunocompromised or with autoimmune disease, and that has not been characterised outside supervised trials. Material sold in the UK under this name is unlicensed and unverified for identity and purity.
Mechanism of action
How Thymosin Alpha-1 works
N-terminally acetylated 28-amino-acid peptide originally isolated from thymic tissue and produced synthetically. Described in the literature as an immunomodulator acting largely through Toll-like receptor signalling on dendritic cells and on T-cell maturation, rather than as a direct antiviral or antimicrobial agent. Distinct in sequence and in mechanism from Thymosin Beta-4 and its fragment TB-500, which are actin-binding molecules and are frequently conflated with it in vendor copy.
Top peer-reviewed citations
Selection of the most-cited peer-reviewed literature on Thymosin Alpha-1. Where a verified PMID or DOI is shown, the citation links to the original record. Other citations list the title, authors, journal and year so the reader can locate the paper through the journal index or the PubMed search linked below. PeptideClear publishes editorial commentary, not clinical guidance.
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Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma
Maio M, Mackiewicz A, Testori A, et al.. Journal of clinical oncology : official journal of the American Society of Clinical Oncology, 2010.
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Combination of entecavir with thymosin alpha-1 in HBV-related compensated cirrhosis: a prospective multicenter randomized open-label study
Wu X, Shi Y, Zhou J, et al.. Expert opinion on biological therapy, 2018.
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A Pilot Trial of Thymalfasin (Thymosin-alpha-1) to Treat Hospitalized Patients With Hypoxemia and Lymphocytopenia Due to Coronavirus Disease 2019 Infection
Shehadeh F, Benitez G, Mylona EK, et al.. The Journal of infectious diseases, 2023.
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The efficacy of thymosin alpha-1 therapy in moderate to critical COVID-19 patients: a systematic review, meta-analysis, and meta-regression
Soeroto AY, Suryadinata H, Yanto TA, et al.. Inflammopharmacology, 2023.
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The efficacy and safety of thymosin alpha1 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.
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Thymosin alpha 1 alleviates inflammation and prevents infection in patients with severe acute pancreatitis through immune regulation: a systematic review and meta-analysis
Tian Y, Yao J, Ma Y, et al.. Frontiers in immunology, 2025.
Full PubMed search: https://pubmed.ncbi.nlm.nih.gov/?term=thymosin+alpha+1+thymalfasin.
Registered clinical trials
As of 2026-07-13, no interventional trials for Thymosin Alpha-1 are listed on ClinicalTrials.gov or the ISRCTN registry. This is itself informative: much of the Thymosin Alpha-1 evidence base is preclinical, which is why the evidence grade above matters.
Source: ClinicalTrials.gov and the ISRCTN registry, refreshed 2026-07-13. See the peptide clinical-trials tracker for the full picture across compounds.
UK regulatory status
Plain-English summary of where Thymosin Alpha-1 sits under the four UK and international frameworks that govern peptide supply. Editorial commentary, not legal advice.
- Misuse of Drugs Act 1971: Not controlled under the Misuse of Drugs Act 1971.
- Psychoactive Substances Act 2016: Not scheduled under the Psychoactive Substances Act 2016.
- MHRA medicines classification: No UK marketing authorisation as a medicine.
- WADA Prohibited List: Not currently listed on the WADA Prohibited List.
Risks and unknowns
What the literature does not yet show about Thymosin Alpha-1
Known concerns
- Thymosin Alpha-1 has been studied in randomised human trials, which is a materially stronger position than most compounds on this site. Trial populations, endpoints and durations are still narrower than everyday use, so results describe the trial, not every person.
- The body of published work on Thymosin Alpha-1 is small, at 6 papers in our record. A thin literature means individual findings carry more weight than they should, and one contrary result can change the picture.
- There are no registered interventional clinical trials for Thymosin Alpha-1 on ClinicalTrials.gov or the ISRCTN registry. Nobody is currently running the study that would answer the safety and efficacy questions.
- Thymosin Alpha-1 holds no UK marketing authorisation, so nothing you can buy has been assessed by a regulator, released by batch, or dispensed by an accountable pharmacy. Purity, dose accuracy and sterility rest entirely on the seller's own documentation.
Open questions in the literature
- Long-term outcomes beyond the duration of the published trials are unknown, and the published trials are considerably shorter than the periods over which people actually use these compounds.
- Interactions between Thymosin Alpha-1 and prescribed medicines are not systematically studied, which matters most for anyone already on treatment for a long-term condition.
- Immune modulation cuts both ways by definition, and the conditions under which a given effect would be unwanted are not well mapped.
Regulatory note
No UK marketing authorisation as a medicine. Not currently listed on the WADA Prohibited List. The moment a UK seller or commentator makes a therapeutic claim, MHRA can treat the product as an unlicensed medicinal product.
Important: PeptideClear publishes encyclopedia commentary only and does not recommend human use. Speak to a UK-registered prescriber before any medical decision.
Related reading on PeptideClear
Frequently asked questions
What is the evidence level for Thymosin Alpha-1?
What is the UK regulatory status of Thymosin Alpha-1?
Has Thymosin Alpha-1 been tested in human clinical trials?
Where can I read the source literature for Thymosin Alpha-1?
Last verified 2026-07-19. Editorial commentary, not legal or clinical advice. Citations without a linked identifier can be located through the PubMed search and the journal index.