What exactly causes ADHD?

The exact causes of ADHD are not known. There have been several theories throughout history, but none have been proven by empirical science. Recent research shows ADHD is partially genetic, meaning it is passed along in families. Keep in mind that just because it is genetic does not mean that every family member will have ADHD. Epigenetics comes in to play with ADHD, as there are certain genetic and environmental factors which interact and likely causes the expression of ADHD more likely in certain individuals, The causes or factors leading to expression of ADHD is not currently known.

Chemical imbalances in the brain. That is why some people take medications from a psychiatrist, the medications will alter the chemicals in your body, usually balancing them out.