This proposed study is the first study to systematically address the reduction of antipsychotic polypharmacy to monotherapy in patients with primary psychotic disorders in a prospective, double-blind, placebo-controlled design. The results of this study will have important implications for the clinical practice of physicians treating the severely mentally ill who are often constrained to practice beyond the limits of available clinical guidelines and evidence based medicine. Thus, in light of the high and growing prevalence of this practice, the proposed study speaks to a real and practical clinical dilemma within this field. Furthermore, as a university-based, tertiary care psychiatric centre serving thousands of severely ill patients suffering from primary psychotic disorders and with an established track record for innovative clinical research, we are uniquely placed to address these critical questions.