The purpose of this project is to evaluate the effectiveness of a structured aerobic exercise intervention for adults with Attention-Deficit/Hyperactivity Disorder (ADHD) with and without medication and compare it to medication alone. Participants will be randomly assigned to medication only + education, aerobic exercise intervention only, and combined aerobic exercise and medication groups. Participants will be evaluated at baseline, following medication optimization (for medicated groups), following 8 weeks of intervention, after 3 months of follow-up, and after 6 months of follow-up. The investigators hypothesize that the combined group will have the best outcome at all evaluation points and that treatment gains will be maintained throughout the follow-up period if the assigned treatments are continued.