CYP2D6 and schizophrenia: Accordingly, CYP2D6 genotyping might be helpful for risperidone level assess, researchers found that CYP2D6 poor metabolizers had greater dose-adjusted levels of risperidone and total active moiety, and higher RIP/9-OH-RIP ratio and lower dose-corrected 9-hydroxyrisperidone levels in first-episode drug-naïve schizophrenia patients, thereby indicating a lack of CYP2D6 activity [29].