<qa>  What is the only antipsychotic drug approved for treatment resistant patients with schizophrenia?Clozapine is the only antipsychotic drug that has been approved for treatment resistant patients with schizophrenia. However, up to 50 of patients treated with clozapine fail to respond and continue to exhibit clinically significant residual positive and negative symptoms and cognitive impairments. An emerging trend in treatment is the addition of a second antipsychotic drug. This study will determine if risperidone when given as adjunctive treatment is more effective than placebo in treating schizophrenic patients failing clozapine therapy. 