1) Attention deficit hyperactivity disorder (ADHD) is a brain disorder characterized by inattention, hyperactivity, and impulsivity that interferes with functioning. 2) While the specific causes are unknown, genetic and environmental factors like smoking during pregnancy may play a role. ADHD is associated with lower dopamine levels in the brain. 3) Diagnosis involves evaluating symptoms like poor attention, hyperactivity, and impulsivity based on reports from parents and teachers. Stimulant medications and behavioral therapy are commonly used to treat ADHD.