Thymosin alpha-1
Thymic peptide immunomodulator
Status
Approved elsewhere
Approved as Zadaxin in China since 1996, in Italy and in more than 30 countries (mainly for chronic hepatitis B) but never by FDA or EMA; in the US its compounding nomination was withdrawn in 2024 and an FDA advisory committee then voted 17 to 4 against adding it to the 503A bulks list.
Evidence
Moderate
Many human trials exist, including a large 2025 sepsis RCT, but results are mixed and FDA judged efficacy unproven for every use it reviewed.
Thymosin alpha-1 (thymalfasin) is a 28-amino-acid peptide first isolated from the thymus that modulates immune responses. It is approved as Zadaxin in China, Italy and other countries, mainly for hepatitis B, but not in the US or EU.
Structure
28 residuesPoint at a bead, or focus the chain and use the arrow keys, to name it. Pick a chemistry to highlight it.
Sequence as text
Ac-S-D-A-A-V-D-T-S-S-E-I-T-T-K-D-L-K-E-K-K-E-V-V-E-E-A-E-N-OH
What it is used for
- Chronic hepatitis B, in China and other countries outside the US and EU (approved)
- Hepatitis C and as a vaccine or chemotherapy adjuvant, in certain countries (approved)
- Sepsis, where a 1,106-patient trial found no mortality benefit (studied)
- COVID-19, HIV and several cancers (studied)
- General immune support, chronic fatigue and Lyme disease (claimed, unproven)
How it works
Thymosin alpha-1 was first isolated from calf thymus in 1977. FDA's 2024 review describes its immune-modulating effects as mediated at least partly through Toll-like receptor 9 (TLR9) on dendritic cells and lymphoid progenitor cells. In rodent models it suppressed tumour growth, viral infections and sepsis, and it raised antibody responses to some vaccines in mice. After injection under the skin in healthy men it peaks at about 2 hours and does not accumulate with daily dosing.
How strong the evidence is
Moderate
FDA's December 2024 review covered hepatitis B and C, HIV, COVID-19, vaccine response, cancers, sepsis and other uses and found effectiveness unestablished for all. In hepatitis B, trials of thymosin alpha-1 alone gave mixed results and a randomised open-label trial adding it to entecavir showed no clear gain. In hepatitis C, a double-blind trial adding it to peginterferon and ribavirin did not improve response. The largest trial, TESTS (BMJ 2025), randomised 1,106 adults with sepsis in China: 28-day mortality was 23.4% versus 24.1% on placebo. The FDA advisory committee voted 17 to 4 against its use in compounding.
Risks and side effects
- Injection-site irritation, redness and discomfort are the most commonly reported effects.
- Liver enzyme (ALT) flares in hepatitis B and thyroid (TSH) abnormalities in hepatitis C have been reported in trials.
- In stem cell transplant recipients, fatal immune haemolytic anaemia and engraftment failure have been reported, and it may worsen graft-versus-host disease in deliberately immunosuppressed patients.
- Foreign labels carry warnings for children, pregnancy, breastfeeding, autoimmune disease and immunosuppression.
- Compounded or grey-market products carry immunogenicity and impurity risks, according to FDA.
Regulatory status
| Region | Year | Approved for |
|---|---|---|
| CNChinese drug regulator (now NMPA) | 1996 | Chronic hepatitis B |
Status by country
| Jurisdiction | Status | Source |
|---|---|---|
| USUnited States | No authorised medicine | Source 2 |
| EUEuropean Union | Authorised in some member states | Source 10 |
| UKUnited Kingdom | No authorised medicine | Source 11 |
| AUAustralia | No authorised medicine | Source 12 |
| CACanada | No authorised medicine | Source 13 |
Trials of Thymosin alpha-1 to watch
Thy-α1 for RIF(opens the source in a new tab)
Thymosin-α1 for Recurrent Implantation Failure
Thymosin alpha-1 in colorectal cancer(opens the source in a new tab)
Thymosin-alpha 1 for Adjuvant Treatment After Radical Resection of High-risk Stage II and III Colorectal Cancer
Thymosin alpha-1 in lung cancer(opens the source in a new tab)
The Impact of Thymosin α-1 on the Efficacy of Concurrent Chemoradiotherapy Followed by Immunotherpay Consolidation for Locally Advanced NSCLC
Timeline
2027
2026
1996
- Approved, CN (Chinese drug regulator (now NMPA))Chronic hepatitis B
Sources
- 01Summary Minutes, December 4, 2024 Meeting of the Pharmacy Compounding Advisory Committee(opens the source in a new tab)
- 02Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances: FDA presentation to the Pharmacy Compounding Advisory Committee(opens the source in a new tab)
- 03The efficacy and safety of thymosin alpha1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial(opens the source in a new tab)
- 04PubChem Compound Summary: Thymalfasin (CID 16130571)(opens the source in a new tab)
- 05UniProtKB P06454: Prothymosin alpha (PTMA), human(opens the source in a new tab)
- 06SciClone Pharmaceuticals Form 10-K for fiscal year 2004(opens the source in a new tab)
- 07SciClone Pharmaceuticals: Selling Specialty Drugs in China(opens the source in a new tab)
- 08Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks(opens the source in a new tab)
- 09World Anti-Doping Code International Standard: Prohibited List 2026(opens the source in a new tab)
- 10ZADAXIN 1,6 mg/ml polvere e solvente per soluzione iniettabile(opens the source in a new tab)
- 11MHRA Products: active substances beginning with T(opens the source in a new tab)
- 12Australian Register of Therapeutic Goods (ARTG)(opens the source in a new tab)
- 13Unauthorized injectable peptide drugs seized from Optimum Wellness Centre in Calgary, Alberta may pose serious health risks(opens the source in a new tab)
Educational information, not medical advice. Talk to a licensed clinician before starting, stopping or changing any medicine.