[Page 327]Attention-deficit/hyperactivity disorder (ADHD) is a prevalent and impairing mental health disorder, with typical onset in childhood. Listed as a “neurodevelopmental disorder” in the fifth edition of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-5), ADHD is defined by the presence of developmentally extreme and significantly impairing levels of (a) inattentive behavior patterns, (b) hyperactive-impulsive behavior patterns, or (c) both. Once believed to be restricted largely to middle-class boys in the United States, ADHD is now known to exist around the developed world in both males and females, in individuals spanning the socioeconomic spectrum, and in people from all racial/ethnic groups. Its impairments persist into adolescence and adulthood in a majority of instances. Exhibiting a substantial genetic liability, with additional roots ...