In this study, we are conducting a randomized double blind trial of risperidone treatment for psychotic patients who are admitted to inpatient units due to acute relapse. We anticipate to recruit 264 subjects and test their CYP2D6 polymorphism genotypes, based on which they will be randomly assigned to either a low dose slow titration group or a treatment as usual group. They will be assessed every five days for 15 days, and then at follow-ups at 4-weeks and 6-weeks from study entry.