This study is enrolling individuals who are in their first episode of schizophrenia or schizoaffective disorder and who are currently using cannabis. Study participants undergo a screening visit including the Structured Clinical Interview for DSM-IV for diagnostic evaluation, and a physical examination, blood tests, and review of medical, psychiatric, and substance use history. Following the screening visit, eligible participants are randomly assigned to single-blind treatment with clozapine or risperidone for 24 weeks. Participants assigned to clozapine initially receive a daily dose of 12.5 mg, which is carefully titrated to the lowest dose necessary to manage psychotic symptoms and well tolerated. Participants assigned to risperidone initially receive 0.5 mg daily and are carefully titrated in the same fashion. Cross titration off of the previous antipsychotic (if any) and onto study medication is completed within 2-4 weeks. Participants on clozapine have weekly blood tests. Concomitant medications are minimized and kept stable throughout the protocol except as needed to manage side effects or urgent clinical symptoms. Study medication, psychiatric visits, assessments and labwork are all provided without charge to participants. Study visits take place once a week. At study visits, medication side effects, physical and psychiatric symptoms, substance use, and treatment services received are assessed. A Lifestyle Intervention is also provided to help prevent metabolic side-effects in this vulnerable population, and assist with recovery. The investigators meet weekly to review clinical care and manage any variations in study protocol.