* Clozapine is generally considered to be more effective than other antipsychotic drugs. Clozapine is often used in treatment-resistant schizophrenia (poor treatment response to 2 or more antipsychotic drugs). So a switch from clozapine to another antipsychotic drug could cause problems regarding efficacy.<ref> McEvoy J P et. al,[http://ajp.psychiatryonline.org/cgi/reprint/163/4/600]. Am J Psychiatry 2006; 163:600–610. </ref>