# Thymosin alpha-1

A thymus peptide that nudges T cells. Approved in more than 35 countries for hepatitis and as an immune booster in illness, but never in the US. Its largest modern trial was negative.

Also called: Thymalfasin, Zadaxin, Tα1
Source page: https://peplogue.com/peptides/thymosin-alpha-1/
Updated: 2026-10-22. Not medical advice.

## How it works

- Where it acts: Toll-like receptors on immune cells.
- What it changes: It helps T cells mature and boosts immune signalling.
- What people notice: Used as an add-on for hepatitis B and in cancer care in some countries. Few side effects, and inconsistent benefit.

## What the evidence shows

- **General immune boosting in healthy people**: Lab only. Not studied.
- **Hepatitis B and C (add-on)**: Early. Older trials are mixed. In the largest hepatitis C trial, of 552 patients whose earlier treatment had failed, adding it made no overall difference (12.7% cleared the virus, against 10.5%). A gap of 41% against 26% appeared only in the third who finished the course. Modern antivirals have replaced it.
- **Sepsis**: Failed. A 1,106-patient double-blind trial in China (BMJ, 2025) found no difference in deaths at 28 days: 23.4% against 24.1%.
- **COVID-19**: Early. Observational studies conflict, and an apparent benefit vanished after adjusting for patient differences. No large randomized trial.

## Side effects and risks

- common: Irritation at the injection site.
- unknown: It stimulates the immune system.
- unknown: FDA calls the safety information for compounded versions inadequate.

Who should avoid it: Transplant recipients and people on immune-suppressing treatment, unless a specialist advises it.

## How it has been given in studies

Hepatitis trials used 1.6 mg injected under the skin twice a week. Other studies ranged from 0.8 mg to 6.4 mg.

## Legal status

- United States: undefined. Its compounding nomination was withdrawn. FDA advisers reviewed it in December 2024.
- European Union: undefined. No EU-wide approval. Zadaxin appears in Italian drug listings, which we have not verified.
- Spain: undefined. No thymalfasin medicine in CIMA (searched by ingredient and as Zadaxin), so it is not authorised in Spain. Not lawful to sell to the public.
- Germany: undefined. Not verified for Germany. No German approval confirmed; Italian listings of Zadaxin unchecked. Unapproved sale would be unlawful.
- France: undefined. Not verified. No French authorisation found, but the national drug database could not be searched.
- Italy: undefined. Zadaxin 1.6 mg (SciClone Italy): classe C, repeatable prescription, you pay. AIFA data show it authorised; current marketing not confirmed.
- Netherlands: undefined. Not verified. No Dutch listing found in the Farmacotherapeutisch Kompas and the CBG database could not be checked.
- United Kingdom: undefined
- Canada: undefined
- Australia: undefined

## Questions people ask

**Does thymosin alpha-1 boost the immune system?**

It helps T cells mature and boosts immune signalling, but general immune boosting in healthy people has not been studied. Its largest modern trial, in 1,106 patients with sepsis, found no difference in deaths at 28 days.

**Is thymosin alpha-1 FDA approved?**

No. It is approved in more than 35 countries for hepatitis and as an immune booster in illness, but never in the US, and its US compounding nomination was withdrawn.

**Does thymosin alpha-1 help with COVID-19?**

Observational studies conflict, and an apparent benefit vanished after adjusting for patient differences. There is no large randomized trial.

**Who should avoid thymosin alpha-1?**

Transplant recipients and people on immune-suppressing treatment, unless a specialist advises it. It stimulates the immune system, and FDA calls the safety information for compounded versions inadequate.

## Sources

- TESTS trial 2025: thymosin alpha-1 for sepsis: https://scholar.xjtu.edu.cn/en/publications/the-efficacy-and-safety-of-thymosin-%CE%B11-for-sepsis-tests-multicent/
- Ciancio et al. 2012: thymosin alpha-1 added to hepatitis C treatment: https://doi.org/10.1111/j.1365-2893.2011.01524.x
- Tao et al. 2023: review of thymosin alpha-1: https://www.mdpi.com/1420-3049/28/8/3539
- Partnership for Safe Medicines: peptide import records (9 Jun 2026): https://www.safemedicines.org/2026/06/fishy-peptide-freight.html
- FDA: bulk substances that may present significant safety risks: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks