The investigators are proposing to test a medication derived from our prior studies of the gene SLC9A9. This one gene makes NHE proteins that control how we learn and remember items, which is impaired in ADHD and may cause an inability to plan, prioritize, self-monitor,inhibit, initiate, self-correct, or control one's behavior. The investigators now propose to investigate the therapeutic utility of an NHE inhibitor, amiloride hydrochloride, for the treatment of attention deficit hyperactivity disorder (ADHD) in medication-naïve adults with ADHD.