High rates of ADHD have been reported in adolescents with SUD. In addition, untreated ADHD is a risk factor for developing SUD. Atomoxetine is a norepinephrine reuptake inhibitor, and is currently used to treat adolescents with ADHD. The purpose of this trial is to evaluate the efficacy of atomoxetine in treating adolescents dually diagnosed with ADHD and SUD.