Is ADHD a mental impairment?

It is a functional i. To get any "diagnosis " there needs to be functional impairment, if there is no impairmant then it does not warrant a diagnosis.
No. Adhd is a neurobiologic disorder inherited in most cases causing problems with executive brain function. This results in academic underachievement, poor interpersonal relationships. Increased risk for drug & nicotine abuse, employment & financial problems, procrastination, disorganization, forgetfulness, marital difficulties, motor vehcile accidents, and employment problems.