Thymosin Alpha-1

Overview

Thymosin alpha-1 is a thymic peptide (28 amino acids) used in many countries for immune modulation, hepatitis B and C, immune deficiency, and as an adjunct in cancer therapy. It is marketed outside the US as Zadaxin and is approved in over 35 countries with clinical trial support. In the US it is not FDA-approved. Its nomination was withdrawn from the 503A Category 2 list in September 2024—so it is not on the active Category 2 list, but that does not automatically create a legal compounding pathway. The FDA has issued warning letters when thymosin alpha-1 was offered to treat COVID-19. Status in the US remains complex. Evidence outside the US is strong; in the US, use is not approved and patients should not assume it is legally available without consulting a lawyer or licensed pharmacy.

How It Works (Mechanism of Action)

Thymosin alpha-1 modulates immune function, supporting T-cell maturation and response. It has been studied in viral infections, immune deficiency, and oncology support abroad.

Primary Uses

Immune modulation, hepatitis B/C, immune deficiency, cancer adjunct (abroad). Not FDA-approved in the US. Do not use for COVID-19; FDA has warned against this.

FDA & Regulatory Status

Complex. Not FDA-approved in the US. Nomination withdrawn from 503A Category 2 (September 2024). Marketed as Zadaxin in 35+ countries. FDA warning letters when offered for COVID-19. Confirm current US status with a lawyer or pharmacy.

Last reviewed February 2026.

Clinical Evidence

Strong outside the US—approved in multiple countries with clinical data. In the US, not approved for any use.