Attention deficit hyperactivity disorder (also known as ADHD or ADD) is one of the most frequently occurring childhood psychiatric disorders. It affects an estimated 4.1 percent of youths ages 9 to 17 in a six-month period. Common symptoms include difficulty staying focused on a task, having trouble sitting still, and acting without thinking. Symptoms usually become evident in preschool or early elementary years, and can continue into adolescence and even adulthood. In many cases, the most effective treatments for ADHD include medications and behavioral therapies.