Treatment of Schizophrenia and Comorbid Cannabis Use Disorder: Comparing Clozapine to Treatment-as-Usual

Individuals with schizophrenia have a high risk of becoming addicted to drugs; between 13 to 42% of schizophrenics are addicted to marijuana. These individuals often have difficulties adhering to a substance abuse treatment program, and have an increased chance of marijuana relapse. Marijuana use by schizophrenics has also been associated with clinical exacerbations, noncompliance with antipsychotic medications, poor global functioning, and increased rehospitalization rates. While antipsychotic medications are often effective in controlling symptoms of schizophrenia, they are not always effective in preventing substance abuse. Clozapine, an atypical antipsychotic drug, is currently used to treat schizophrenia. Preliminary research has shown that clozapine is more successful at reducing drug relapse rates in individuals with schizophrenia, as compared to other antipsychotic medications, including olanzapine and risperidone. The purpose of this study is to compare the effectiveness of clozapine as compared to other oral antipsychotic treatment, including combinations of up to two antipsychotics, in reducing marijuana use in schizophrenic individuals. This study will enroll individuals with schizophrenia who are currently taking any oral antipsychotic other than clozapine, including those taking up to two oral antipsychotic, and who are also addicted to marijuana. The study will begin with a 1-week assessment phase, during which all participants will continue taking olanzapine or risperidone. Participants will undergo a physical examination and have blood drawn for laboratory tests. Information pertaining to their medical, psychiatric, and substance use history will also be collected. Urine tests and breathalyzers will be used to screen for the presence of alcohol and drugs. Following the assessment phase, participants will be randomly assigned to switch to clozapine or remain on their prestudy antipsychotic for 12 weeks. Participants remaining on their prestudy antipsychotic treatment will continue to receive the same dose for the entire study. Participants taking clozapine will initially receive a daily dose of 12.5 mg, which will be increased to a maximum of 400 mg per day, as tolerated. Study visits will take place once a week. At each visit, medication side effects, physical and psychological symptoms, substance use, treatment services received, and living situation will be assessed. Blood will be drawn for laboratory tests. Drug and alcohol levels will be monitored three times a week through urine and breathalyzer tests. Quality of life questionnaires will be administered once a month.