Review · United States
Thymosin alpha-1
Reviewed on
Approval and product status
No FDA-approved thymosin alpha-1 product was identified in the United States as reviewed August 30, 2026
FDA treats the free base and its acetate salt as different chemical forms. FDA's 2024 review described Zadaxin as a finished medicine with narrow approval outside the United States. The ingredient name alone does not identify that product. No FDA-approved U.S. product was found.
What was measured in people?
- Health results · Moderate
- A large randomized sepsis study found no clear drop in 28-day deaths. FDA found that the wider disease evidence did not establish a benefit.
- Body changes · Moderate
- Studies in people measured how it moved through the body and changed blood tests tied to the immune system. These findings do not establish a general health benefit.
A change in a hormone or body signal does not by itself prove a health benefit.
Important limits
This tool is not an independent medical review. It does not recommend treatment.
FDA says compounded thymosin alpha-1 may cause unwanted immune reactions. FDA also flags impurities and problems with confirming the active ingredient. The available data cannot define every risk. This guide gives no dosing, injection, sourcing, or treatment instructions.
Still unknown: FDA reviewed proposed uses that included viral liver disease, cancer, sepsis, COVID-19, vaccine response, lung disease, and other conditions. FDA found too little reliable evidence to show that it worked for the uses it reviewed. The records do not show a general “immune boost,” infection prevention, long-COVID benefit, or anti-aging effect. They also do not show that an online or compounded product matches study material.
This record cannot check a package, seller, batch, or personal treatment. It does not provide sport clearance.
Approval fact checks
“Thymosin alpha-1 is FDA-approved in the United States.”
Misleading. FDA says no approved U.S. drug contains thymosin alpha-1 free base or its acetate salt. Foreign product status does not create U.S. approval.
Applies to: United States regulatory status as reviewed August 30, 2026.
Products in this review
These are selected records, not every product or form.
No product label record is included here. That is not a separate approval decision. Read the status and sources above.
What the research shows
Sepsis is a dangerous body response to infection. The TESTS study assigned 1,106 adults with sepsis at 22 centers in China to thymosin alpha-1 or placebo by chance. A placebo looks like the study product but has no active ingredient. In the corrected analysis, 23.4% of the thymosin alpha-1 group and 24.1% of the placebo group died within 28 days. This was not a clear difference. Other randomized studies tested severe pancreas inflammation, viral liver disease, and earlier sepsis groups. Their results did not establish a broad treatment benefit.
Read all Thymosin alpha-1 fact checksSources used in this review
A source may support some statements, not all of them. Use the links above or this review to see what each source supports.
Show 11 sources
- FDA identity overview for thymosin alpha-1
U.S. Food and Drug Administration · FDA review · 2024
Source accessed
- FDA review of the separate thymosin beta-4 fragment called TB-500
U.S. Food and Drug Administration · FDA review · 2025
Source accessed
- FDA evaluation of thymosin alpha-1 for pharmacy compounding
U.S. Food and Drug Administration · FDA review · 2024
Source accessed
- FDA list of substances that may present compounding safety risks
U.S. Food and Drug Administration · Regulatory · 2026
Source accessed
- FDA drug approvals and databases
U.S. Food and Drug Administration · Regulatory · 2026
Source accessed
- Large randomized TESTS sepsis trial
The BMJ · Randomized trial · 2025
Source accessed
- Correction to the TESTS sepsis trial
The BMJ · Reference · 2025
Source accessed
- TRACE trial in acute pancreatitis
PubMed · Critical Care · Randomized trial · 2022
Source accessed
- Earlier ETASS sepsis trial
PubMed · Critical Care · Randomized trial · 2013
Source accessed
- Randomized chronic hepatitis B trial
PubMed · Hepatology · Randomized trial · 1999
Source accessed
- 2026 Prohibited List
World Anti-Doping Agency · Anti-doping · 2026
Source accessed