Evidence-based psychosocial treatments have recently been developed. However, very little data exist on the use of pharmacotherapy for adolescents SUD (Substance Use Disorder). One promising pharmacotherapy approach is to treat co-occuring psychiatric disorders. A common co-occurring disorder in adolescent SUD is attention-deficit/hyperactivity disorder (ADHD). Fortunately, new ADHD medications, such as atomoxetine, that do not have addictive potential are now available. However, all controlled studies of atomoxetine have specifically excluded teens with SUD. Therefore, little data exist on the safety and efficacy of the medication in this population. This research project will address the important research gap with the specific aim: to conduct a randomized, placebo-controlled trial of atomoxetine for ADHD in teens with SUD.