Phase 4: Six-week Open-Label Phase Subjects will begin Aptensio XR® 10 mg at the morning following Visit 7. Dosing should occur prior to 10 am each morning. At weekly visits (Visits 8-13), dosing may be maintained or increased until an optimal dose or the maximum dose is reached. The ADHD-RS-IV rating scale will be used to determine optimal dose. An optimal dose is a dose that produces a reduction from Visit 7 of ADHD symptoms of at least 30% and a CGI-I compared to Visit 7 of "much improved" or "very much improved" with tolerable side effects. Subjects who meet improvement criteria but may benefit from additional dose increases, may have their dose further optimized. If a higher dose is not tolerated, subjects may step down one dose level. See Section 6.1.1 for a detailed list of procedures.