Thymosin Alpha-1 Research Evidence
The Thymosin Alpha-1 evidence base: trials, journals, and what the data does not yet show.
Approved Abroad, Not in the US
As Zadaxin, Thymosin Alpha-1 is an approved drug in more than 35 countries, including Italy, China, South Korea, and India, for chronic hepatitis B and C and as an immunomodulatory agent, with decades of international clinical use and post-marketing data. It has never completed FDA approval in the United States.
Regulatory and Legal Status
Thymosin Alpha-1 is not FDA-approved in the US. As of a February 2026 reclassification, it holds FDA 503A Category 2 status, meaning it can legally be dispensed in the US only by prescription through a licensed compounding pharmacy, a different (and more regulated) pathway than an unapproved research chemical, but still short of full FDA drug approval. Verify any US source is a licensed compounding pharmacy operating under a valid prescription.