Evidence brief
Thymosin alpha-1
Written and source-checked by Anthony Treviso, founder of The Peptide Field.
Direct answer
Thymosin alpha-1 is a 28-amino-acid peptide studied for immune-related uses. A large study in people with sepsis, a dangerous response to infection, found no clear drop in deaths. It is not an FDA-approved U.S. treatment.
A 28-amino-acid peptide studied in people. A large sepsis trial did not show fewer deaths, and no FDA-approved U.S. product was identified.
- How strong is the evidence?
- Emerging
Some studies in people exist. Important questions remain about benefit, safety, who it helps, or how long the effects last. This is not an approval or recommendation. - What evidence exists?
- Investigational human outcomes
Studies measured health results in people, but the molecule is still being studied and is not approved for that use. Important questions remain. - Sports rules
- No prohibition identified
This review did not find a prohibition in the checked record. This does not clear you to compete.
Reviewed August 30, 2026. Sources and update notes are below.
No sales or dosing advice. This guide explains research. It was not independently medically reviewed, and it does not diagnose, prescribe, or recommend treatment.
Also known as TA1 · Ta1 · Tα1 · Thymalfasin
Words used here
- peptide
- a short chain of amino acids
- investigational
- still being studied and not approved for that use
- outcome
- what the study measured
- molecule
- one specific chemical substance
- placebo
- an inactive treatment used for comparison
- randomized
- assigned to study groups by chance
- compounded
- made for one patient by a pharmacy, or in batches by a permitted outsourcing facility; a compounded drug is not FDA-approved
- amino acid
- a small building block that makes peptides and proteins
More detailProduct and study details
01 · Evidence profile
Four questions about the evidence
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.
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.
The large sepsis study found no clear safety difference, but FDA says important safety questions remain for compounded products.
Study material and Zadaxin do not show what is in an online or compounded product.
02 · Identity
What it is
Thymosin alpha-1 is a peptide with 28 amino acids. It has a small chemical group, called an acetyl group, on one end. Thymalfasin is the lab-made form of the same peptide. It is not thymosin beta-4, and it is not TB-500. Zadaxin is a finished medicine, not another name for every TA1 product.
Scientific group: Immune-signaling peptide. This group name describes the type of molecule or body signal. It does not prove a benefit, safety, or approval.
03 · Exact product
The molecule is not the finished product.
Formulation: The finished product's ingredients and physical form. Route: How the product enters the body. Indication: The approved or studied use and group of people for a product.
None identified in the United States.
- Human research in sepsis and other immune-related conditions
04 · Research results
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.
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.
Exact product
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.
05 · Claim check
Claims I checked
4 claims checked for this brief.
“Thymosin alpha-1 has been studied in randomized human trials.”
Yes. Randomized studies tested thymosin alpha-1 in people with specific illnesses. This only means human trials exist. It does not mean that they showed a benefit.
- Evidence used
- Randomized human outcomes. This answer uses a study that assigned people to groups by chance and measured a health outcome.
- Limits of this answer
- The exact study products and groups of people with each illness. A result from one illness does not transfer to another. This answer covers only the named molecule and finished product. It also covers the product form and how people used it. The study limits include who took part, what was used for comparison, what changed, and how long the study lasted.
“Thymosin alpha-1 reduced 28-day deaths in the large TESTS sepsis trial.”
The corrected result was 23.4% with thymosin alpha-1 and 24.1% with placebo. The study found no clear difference in 28-day deaths.
- Evidence used
- Randomized human outcomes. This answer uses a study that assigned people to groups by chance and measured a health outcome.
- Limits of this answer
- The TESTS study randomized 1,106 adults with sepsis at 22 centers in China. The corrected analysis applies only to this study and outcome. This answer covers only the named molecule and finished product. It also covers the product form and how people used it. The study limits include who took part, what was used for comparison, what changed, and how long the study lasted.
“Thymosin alpha-1 is FDA-approved in the United States.”
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.
- Evidence used
- Regulatory or product record. This answer uses an official regulator record or a specific product label.
- Limits of this answer
- United States regulatory status as reviewed August 30, 2026. This answer covers only the named molecule and finished product. It also covers the product form and how people used it. The study limits include who took part, what was used for comparison, what changed, and how long the study lasted.
Show 1 more claim checks
“Every product sold as thymosin alpha-1 is equivalent to Zadaxin.”
FDA's 2024 review describes Zadaxin as a finished medicine with narrow foreign approval. It is not the same as an ingredient name, a compounded product, or an online product.
- Evidence used
- Regulatory or product record. This answer uses an official regulator record or a specific product label.
- Limits of this answer
- The exact product, ingredient form, way it was made, and country status all matter. This answer covers only the named molecule and finished product. It also covers the product form and how people used it. The study limits include who took part, what was used for comparison, what changed, and how long the study lasted.
06 · Questions
Questions people ask about Thymosin alpha-1
No FDA-approved thymosin alpha-1 product was identified in the United States as reviewed August 30, 2026. No approved product is identified in the United States.
No prohibition identified. Thymosin alpha-1 is not named in the reviewed 2026 WADA list. Thymosin beta-4 and TB-500 are different substances and are named. This is not personal clearance. Athletes must check the current list and their sport rules. This status is not personal clearance to compete.
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.
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.
07 · Safety
Safety limits for this record
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.
Thymosin alpha-1 is not named in the reviewed 2026 WADA list. Thymosin beta-4 and TB-500 are different substances and are named. This is not personal clearance. Athletes must check the current list and their sport rules.
This review did not find a prohibition in the checked record. This does not clear you to compete.
Reviewed .Check current rules for tested sport ↗Open the governing record ↗08 · Sources
Read the sources
09 · Review history
Review history
Initial brief reviewed FDA identity and compounding records, randomized human trials, corrected sepsis results, and the 2026 World Anti-Doping Agency list.
Written and source-checked by Anthony Treviso, founder of The Peptide Field.
Not independently medically reviewed. This page is not a dosing, sourcing, or treatment guide.