CYP2D6 and schizophrenia: Risperidone (RIS) is an atypical antipsychotic (AAP) drug that is prescribed for the treatment of autism, schizophrenia, and acute bipolar mania, which is metabolized by the CYP2D6 enzyme in the liver to its major active metabolite, 9-hydroxyrisperidone (9-OH-RIS, also known as paliperidone).