Attention deficit hyperactivity disorder, or ADHD, is a common condition that, for a lot of people, is difficult to treat. The drugs that exist have a number of adverse side effects, and about 25 percent of patients don’t respond to existing drugs. And so a team of researchers in Iceland, led by Karl Karlsson, professor of biomolecular engineering at Reykjavik University, undertook a number of different steps to narrow in on and then test what the team has determined to be a novel treatment for ADHD, using an existing drug, amlodipine.