The purpose of this study is to determine whether the medication atomoxetine, or Strattera, plus 3 sessions of counseling can help people to reduce the symptoms of ADHD and to help cut back on their marijuana use. Participation in the study is approximately 12 weeks of medication treatment and doctor's visits once a week. The first 2 visits consist of evaluations to determine if you qualify to participate. These visits are approximately 2-3 hours long and will include questions about your past and present substance use, psychiatric history, a routine physical exam, bloodwork, and paper and pencil questionnaires about your marijuana use. Once you are enrolled in the study, visits are typically 30 minutes long, once a week. The one-on-one counseling sessions regarding marijuana use are 1 hour long and you will have 3 sessions throughout the study. If you qualify for this study, you will receive either atomoxetine, or a placebo (sugar pill). Study participants will have a 50% chance of receiving atomoxetine. Atomoxetine is a non-stimulant, commonly used to treat ADHD.