Thymosin alpha-1
Reviewed
Short 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.
The Peptide Field explains research. Its pages are not independently medically reviewed, and they do not diagnose, prescribe, or recommend treatment.
Read the study findingsAlso known as TA1 · Ta1 · Tα1 · Thymalfasin
Legal status Is Thymosin alpha-1 legal? See the status table
Study and product details
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.
Type of peptide: Immune-signaling peptide. This describes what the substance is or how it works. It does not show that it is safe, effective, or approved.
What has been studied?
- Moderate: Useful evidence exists, but important limits remain.
- Limited: Research is too small or incomplete, or does not directly answer this question.
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.
Products with the same ingredient can differ.
The ingredient name does not tell you everything about a product. Check its other ingredients, its form, how it enters the body, and the use and people covered by the research or approval.
None identified in the United States.
- Human research in sepsis and other immune-related conditions
Have a lab test report (COA) for a product sold under this name? Check what the report shows in 10 questions
Not sure if a product sold under this name is a prescription, compounded, or research-only vial? Sort it in 5 questions
What studies found
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.
Which products do these findings apply to?
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.
Thymosin alpha-1 side effects and safety: what FDA has said
This page has no trial or drug-label side-effect table for Thymosin alpha-1. FDA keeps a page of bulk substances that may be risky when a pharmacy mixes (compounds) them. Here is what that page says about Thymosin alpha-1, in plain words.
FDA's page does not name specific side effects for Thymosin alpha-1.
FDA's entry is about compounded thymosin alpha-1. It is not a review of Zadaxin, a product approved outside the United States.
- FDA says the safety information is not enough to understand how large any safety problems are.
- FDA says the risk of an immune reaction may be significant for some ways of giving it.
- Making it may leave unwanted peptide by-products in the product.
- It may be hard to confirm exactly what the main ingredient is.
These points come from FDA's review of compounded drugs. They are not a full list of side effects. Having no reports does not mean a product is safe.
Read FDA's exact words
Thymosin-alpha 1 (Ta1): “Compounded drugs containing thymosin-alpha-1 (Ta1) may pose significant risk for immunogenicity for certain routes of administration and may have complexities with regard to peptide-related impurities and API characterization. The safety-related information is inadequate for the agency to sufficiently understand the extent of any safety issues raised by the proposed compounded drug.”
Source: FDA, Certain bulk drug substances for use in compounding that may present significant safety risks , page dated .
Compare side-effect data across peptides
Report a side effect
You can report a suspected side effect to the FDA at 1-800-FDA-1088 or through FDA MedWatch . If a reaction feels serious, get medical care first.
FDA page checked .
Fact checks
4 statements checked. Read what the results mean.
“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.
- What this answer is based on
- Health results from a study with randomly assigned groups
- 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.
Sources for this fact check (2)
“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.
- What this answer is based on
- Health results from a study with randomly assigned groups
- 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.
Sources for this fact check (2)
“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.
- What this answer is based on
- Official record or product label
- Limits of this answer
- United States regulatory status as reviewed August 30, 2026.
Sources for this fact check (3)
Show 1 more fact check
“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.
- What this answer is based on
- Official record or product label
- Limits of this answer
- The exact product, ingredient form, way it was made, and country status all matter.
Sources for this fact check (1)
Questions people ask about Thymosin alpha-1
FDA's page on risky compounding substances says this about Thymosin alpha-1. It does not name specific side effects for Thymosin alpha-1. FDA's entry is about compounded thymosin alpha-1. It is not a review of Zadaxin, a product approved outside the United States. FDA says the safety information is not enough to understand how large any safety problems are. FDA says the risk of an immune reaction may be significant for some ways of giving it. Making it may leave unwanted peptide by-products in the product. It may be hard to confirm exactly what the main ingredient is. These points come from FDA's review of compounded drugs. They are not a full list of side effects.
Risks and safety limits
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.
Reviewed .Check the rules for athletes ↗Read the official rules ↗Terms used in the studies
- peptide
- a short chain of amino acids
- 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
- outcome
- what the study measured
- amino acid
- a small building block that makes peptides and proteins
Read the sources
Show 11 sources
Review history
Initial brief reviewed FDA identity and compounding records, randomized human trials, corrected sepsis results, and the 2026 World Anti-Doping Agency list.
Not independently medically reviewed. This page is not a dosing, sourcing, or treatment guide.
Report a factual error