Clozapine is a drug used in the management of treatment-resistant schizophrenia. Numerous clinical trials, including randomized double-blind clinical trials and large cohort studies, have revealed that clozapine is more effective than any other antipsychotic drugs. However, the same studies have also shown that this drug has several adverse effects such as an agranulocytosis. Therefore, in Japan, clozapine is approved for administration to only patients with treatment-resistant schizophrenia in whom treatment with other antipsychotic drugs was ineffective. Clozapine is prescribed only at approved institutes that are under the registration called Clozaril Patient Monitoring Service (CPMS), and white blood cell counts and prescription dosage of clozapine are strictly monitored under this service.