Thyroid-Stimulating Hormone Levels Don't Change When Patients Switch Among Generic Levothyroxines

Millions of Americans take generic or brand-name levothyroxine. The American Thyroid Association recommends against switching among levothyroxine preparations from different manufacturers (Thyroid 2014; 24:1670). However, the U.S. FDA's position is that approved generic levothyroxine preparations should be interchangeable. In this study, researchers used a national administrative claims database and compared thyroid-stimulating hormone (TSH) levels found in patients who continued to take the same generic levothyroxine preparation and in those who switched.

Participants were 16,000 adults (mean age, 59) who filled prescriptions for generic levothyroxine between 2008 and 2019 and had a stable dose and a normal TSH level (0.3–4.4 mIU/L). During…