PeptideSearch

Thymosin Alpha-1

Tested in people

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It has been tested in people, but it is not an approved medicine. The studies are usually small.

Compiled and reviewed by the PeptideSearch Editorial Team · Status checked 2026-08-25

Also called Tα1 / Zadaxin / Thymalfasin

A copy of a natural immune signal, tested in people for hepatitis and severe infection. Results are mixed and it is not approved in the US.

The basics

What is it?
A copy of a natural peptide the immune system uses as a signal.
What do we know?
It has been tested in people with hepatitis and with severe infection, and it is used as a medicine in some countries.
What do we still not know?
Whether it clearly helps. Results across studies do not point the same way.

Official status: Not nominated for 503A compounding · Checked 2026-08-25

Can a doctor prescribe this?

Small pharmacy (503A)
Never put forward to FDA
Large outsourcing facility (503B)
Category 3 — not enough evidence sent in

Not FDA approved in the United States. Nobody has put it forward for small-pharmacy (503A) compounding — it does not appear anywhere in the FDA 503A category document — so there is no 503A pathway and no 503A restriction either. Its only appearance is on the separate list for large outsourcing facilities (503B).

503A is a pharmacy making a single prescription for one patient. 503B is a facility making batches. They are governed by separate lists. Where a category is shown, it is a position on the FDA's list of substances that have been put forward and are still being worked through — not the final list, which is set by rulemaking. Category 1 means the FDA does not plan to act against a pharmacy that makes it while the review runs.

Lab suppliers we list: 14

Doses used in research

Taken word for word from the studies and trials listed on this page. This is not a recommendation and not a dose for anyone to take.

This is a sample, not the whole literature.

About 2,000 papers mentioning this compound have been published. We show a selected sample of 82 of them, not the full literature. How we choose them · count checked 2026-08-23

Spot an error? corrections@peptidesearch.org

What has happened so far

  1. 21 March 2025503B

    FDA lists "Thymosin alpha-1" under 503B Category 3: Bulk Drug Substances Nominated Without Adequate Support. This is the only FDA compounding list it appears on; there is no 503A entry. Read from the FDA 503B category document dated March 21, 2025.

    FDA

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