ADHD is an unsophisticated, nonsensical notion though with a long history, it being termed "mental restlessness" in 1700s England, Minimal Brain Dysfunction (MBD) in early 1900s USA (of which a Harvard psychiatrist said that any doctor using this diagnosis had a minimal brain dysfunction), with Attention Deficit Hyperactivity Disorder (ADHD) being its newest incarnation. It has symptoms identical to anxiety and depression which can be associated with every psychological and physical disturbance. Though a large profitable industry has grown up around it. Its belief largely reflects public ignorance of early life psychological development, and the attempt to "neurologize" psychological symptoms and life issues. And check online for the prescribed drugs' potential side effects, which are far from small.
To explain what is termed ADHD further: some children with school learning issues and adults with concentration difficulty do have psychological problems, reflecting what has since the 1960s been understood as Elements of A Borderline Psychotic Psychostructural Organization. Which does not mean "psychotic" or "borderline psychotic" but rather weakness of those basic ego capacities which develop in early childhood and include control of thinking and behavior, mood modulation, development of a sense of self, and others. This requires psychotherapy to heal, to replace the deficient ego capacities with more mature one. These weaknesses are not a present or absent diagnosis but a continuam of strengths and weaknesses which must be assessed through interview.