* 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 Olanzapineclozapine versus olanzapine, Quetiapinequetiapine, and Risperidone risperidone in Patients With Chronic Schizophrenia Who Did Not Respond patients with chronic schizophrenia who did not respond to Prior Atypical Antipsychotic Treatmentprior atypical antipsychotic treatment]. Am J Psychiatry. 2006;163:600–610.</ref>