This study aimed to compare strategies differing in the speed of switching schizophrenic patients to aripiprazole from other antipsychotic agents, with dual administration for 2 weeks and then tapering off the current antipsychotic in fast (within 1 week) versus slow (within 4 weeks) strategies. This 8-week, open-label, randomized, parallel study assigned patients with a primary Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, diagnosis of schizophrenia or schizoaffective disorder to either the fast-switching (n = 38) or slow-switching (n = 41) group. Efficacy assessments at 5 time points included Positive and Negative Syndrome Scale and Clinical Global Impression scale. Safety assessments included extrapyramidal symptoms, metabolic profile, serum prolactin level, QTc interval, and adverse events. Drug concentrations and cytochrome P450 CYP2D6 and CYP3A4 genotypes were also measured. The fast- and slow-switching groups were comparable in demographical and clinical features at baseline and dropout rate. In the intention-to-treat analysis using mixed-effects models, there were significant within-group decreases over time in the Positive and Negative Syndrome Scale total scores (P = 0.03) and its subscores except for positive subscores, whereas no between-group differences were found. A reduction in body weight (P = 0.01) and lower levels of total cholesterol (P = 0.03), triglycerides (P = 0.03), and prolactin (P = 0.01) were noted in both groups but no increase in extrapyramidal symptoms or prolongation of QTc. The blood concentrations of aripiprazole in all patients were in a therapeutic range at day 56, with CYP2D6*10 polymorphisms being associated with aripiprazole concentrations. In conclusion, there is no significant difference between the fast- and slow-switching strategy in terms of improvements in clinical symptoms and metabolic profile in this 8-week study.