Marijuana dependence is the most common illicit substance use disorder in the United States. Its prevalence is highest among adolescents and young adults. Major depressive disorder is one of the most common conditions seen in marijuana dependent individuals. Fluoxetine is an antidepressant medication for treatment of major depression among adolescents and children. The purpose of this study is to determine the effectiveness of fluoxetine in treating adolescents and young people dually diagnosed with major depressive disorder and marijuana dependence.