As the prevalence of cigarette smoking is high in schizophrenia patients (around 70%–80%) and probably even higher in treatment-resistant schizophrenia patients (Ding and Hu, 2021), we believe that the DDI observed in our study between PPIs and clozapine is probably more linked to the CYP2C19 inhibition by PPIs. This evidence concerns the gene CYP2C19 and schizophrenia.