our brain on ADHD By Bonnie Berkowitz and Patterson Clark, Published: June 1, 2015 Up to 11 percent of school-age children and 4 percent of adults are estimated to have attention-deficit/hyperactivity disorder. About 70 percent of those kids (and an unknown but growing number of adults) take medication for it. Scientists don’t know exactly what ADHD is — or why certain drugs improve its symptoms — but most research suggests that it causes signaling problems in the brain. ADHD medications are thought to improve those brain signals.