Thymosin alpha-1

What is thymosin alpha-1 and what is it approved for?

Thymosin alpha-1 (Tα1) is described in the research literature as "a highly conserved 28 amino-acid peptide naturally occurring in the thymus" that plays a role in T-cell maturation [1][4]. Its synthetic version, thymalfasin, sold under the brand name Zadaxin, has been approved by various regulatory agencies for hepatitis B viral infection and as an immune-response enhancer for vaccine recipients with weakened immune systems [1]. In China, the same review notes it has also been widely used in people with cancer and severe infections [1].

Is thymosin alpha-1 FDA-approved in the US?

No. FDA's briefing document for its December 2024 compounding advisory committee meeting states that "FDA has approved no drug products containing Ta1" [4]. Separately, FDA's compounding page lists "Thymosin-alpha 1 (Ta1)" among bulk substances nominated for compounding but later withdrawn by the nominator; FDA's entry cites "significant risk for immunogenicity" and safety information the agency called inadequate to evaluate [3]. A 2006 study gave 62 patients with chronic hepatitis B either thymosin-alpha1 or interferon alpha; complete response was 9 of 29 (31.0%) versus 15 of 33 (45.5%) at study completion, and 14 of 29 (48.3%) versus 9 of 33 (27.3%) after six months' follow-up, neither difference statistically significant (P>0.05) [2].