Thymosin Alpha-1

Thymosin Alpha-1 is a 28-amino-acid peptide originally isolated from bovine thymus fraction 5 by Allan Goldstein and colleagues in 1977. A synthetic version, thymalfasin (brand name Zadaxin, developed by SciClone Pharmaceuticals), has since been studied extensively in clinical settings and is approved in more than 35 countries for the treatment of chronic hepatitis B, as an adjunct to interferon therapy for chronic hepatitis C, and as an immune adjuvant in oncology contexts. Despite this robust international clinical track record, Thymosin Alpha-1 has not received FDA approval in the United States. Its regulatory status in the US means that any material available domestically is sold strictly as research-grade for laboratory research use only and is not authorized for human therapeutic administration. Thymosin Alpha-1 occupies a distinctive position among immune-modulating peptides: it is one of the few peptides in this class with a substantial body of published randomized clinical trial data, multiple systematic reviews, and documented real-world use across approved indications spanning decades. Its profile is meaningfully different from preclinical-only peptides, though US research users should remain aware of the unapproved status domestically.