Last updated 18 September 2026 · SARMs Store editorial team. Products on this site are supplied strictly for laboratory research and are not for human consumption. This guide summarises published research; it is not medical advice and contains no instructions for use. 18+ only.
Thymosin Alpha-1 at a glance
| Class | 28-amino-acid acetylated peptide originally isolated from thymus tissue |
|---|---|
| Discovered | Allan Goldstein's laboratory, 1977 |
| Highest evidence | Licensed as thymalfasin (Zadaxin) in more than 30 countries, mainly for chronic hepatitis B and as a vaccine adjuvant; phase III sepsis trials |
| Studied for | T-cell maturation, dendritic cell activation, immune response in infection and cancer |
| Format | Lyophilised vial (5mg) |
| Storage | 2 to 8°C unopened, away from light |
| UK status 2026 | Research chemical; no UK or EU licence; not named on the WADA list |
What Thymosin Alpha-1 is
Thymosin alpha-1 is a 28-amino-acid peptide first purified from calf thymus by Allan Goldstein's group in 1977. It is produced naturally in the thymus and in other tissues and acts on toll-like receptors on immune cells, promoting the maturation of T cells and the activation of dendritic cells. The synthetic form, thymalfasin, has been a licensed medicine in China, Italy and about thirty other countries since the 1990s under the brand Zadaxin. It is not licensed in the UK, the EU as a whole, or the US.
What the research found
Hepatitis B and C. Thymalfasin is licensed abroad for chronic hepatitis B, usually alongside antivirals, on trials from the 1990s and 2000s showing improved viral clearance in some patient groups. Results in hepatitis C were mixed.
Sepsis. A Chinese multicentre trial (Wu and colleagues, Critical Care, 2013) reported lower 28-day mortality in severe sepsis with thymalfasin added to standard care; a larger confirmatory trial (TESTS) reported in 2024 with a smaller and non-significant effect.
Vaccine adjuvant. Trials in elderly and dialysis patients reported improved antibody responses to influenza and hepatitis B vaccines when thymalfasin was given alongside.
Cancer. Studied as an adjunct in melanoma and lung cancer with some phase II signals and no approved indication.
COVID-19. Several observational and small randomised studies in 2020 to 2021 reported reduced mortality in severe cases; a larger trial did not confirm a benefit.
What is missing. Any UK or EU licence, and any study in healthy adults for general immune support.
Stability, storage and handling
Supplied lyophilised in a sealed vial. Keep unopened vials at 2 to 8 degrees Celsius or frozen for long storage, away from light. Reconstituted solutions degrade over days to weeks. The certificate should show HPLC purity and mass spectrometry identity.
Legal status in the UK, 2026
Not a controlled substance under the Misuse of Drugs Act 1971. Thymalfasin has no UK marketing authorisation, so in the UK it is not a licensed medicine and research-grade thymosin alpha-1 cannot be sold or advertised for human use; supplied strictly for laboratory research. Not named on the WADA Prohibited List.
What to check before buying
Milligrams per vial, HPLC purity, mass spectrometry identity, a batch number matching the certificate, and cold-chain shipping. Every Origin Peptides batch is independently tested and its certificate of analysis is published on the product page and the Lab Testing page.
Frequently asked questions
Is thymosin alpha-1 the same as thymalfasin and Zadaxin?
Yes. Thymalfasin is the generic name of the synthetic peptide, Zadaxin the brand.
Is it a licensed medicine?
In China, Italy and about thirty other countries, mainly for hepatitis B. Not in the UK, EU or US.
How does it differ from thymosin beta-4 (TB-500)?
Different molecules from the same tissue. Thymosin alpha-1 acts on immune cells; thymosin beta-4 binds actin and is studied for tissue repair.
Is thymosin alpha-1 legal in the UK?
Legal to buy and possess as a research compound; not lawful to sell or advertise for human consumption.
Key references
Goldstein AL, Low TL, McAdoo M, et al. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proceedings of the National Academy of Sciences. 1977;74(2):725-729. Wu J, Zhou L, Liu J, et al. The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. Critical Care. 2013;17(1):R8. Dominari A, Hathaway Iii D, Pandav K, et al. Thymosin alpha 1: a comprehensive review of the literature. World Journal of Virology. 2020;9(5):67-78.
Related guides
- TB-500 research guide
- SARMs vs peptides: what the research compares
- How to read a certificate of analysis
- SARMs 101 hub
Research products: Origin Peptides Thymosin Alpha-1 5mg · TB-500 5mg · Full Origin Peptides range · Lab Testing