Most of us have heard about ADHD, or attention deficit hyperactivity disorder, in kids. It’s often cited as a major cause of learning and behavior problems at schools. But what most people, including many doctors, don’t realize is that ADHD is also a big problem in adults. In fact, since the condition is estimated to affect 5% of the population, ADHD may well be the single most common chronic unrecognized mental health disorder in the United States.