* 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 effectiveness.<ref> McEvoy J P et. al, [http://ajp.psychiatryonline.org/cgi/content/full/163/4/600 Effectiveness of Clozapine Versus Olanzapine,Quetiapine, and Risperidone in Patients With Chronic Schizophrenia Who Did Not Respond to Prior Atypical Antipsychotic Treatment]. Am J Psychiatry. 2006;163:600–610.</ref>