Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by excessive amounts of inattention, carelessness, hyperactivity (which evolves into inner restlessness in adulthood), and impulsivity that are pervasive, impairing, and otherwise age-inappropriate. Some individuals with ADHD also display difficulty regulating emotions and suffer from executive dysfunction. For a diagnosis, the symptoms have to cause problems in at least two settings (such as school, home, work, or leisure time) for over six months. In children, problems paying attention may result in poor school performance. ADHD is also associated with other mental disorders and substance use disorders, which can cause additional impairment, especially in modern society. Although people with ADHD struggle to focus on tasks they are not particularly interested in completing, they are often able to maintain an unusually prolonged and intense level of attention for tasks they do find interesting or rewarding; this is known as hyperfocus.