This study investigated if and how CYP2D6 and CYP2C19 metabolizer status of patients with depressive and/or anxiety disorders was associated with 1) switching or discontinuing AD treatment (CYP2D6 substrate users: n = 796); CYP2C19 substrate users: n = 313), and 2) whether there was a significant difference in perceived total side effects between patients with a different metabolizer status. This evidence concerns the gene CYP2D6 and Alzheimer disease.