Maybe he has sleep apnea:
http://www.nhlbi.nih.gov/health/dci/Diseases/SleepApnea/Slee...
This would mean no matter how much sleep, it's never enough.
By the way, there is considerable evidence that a significant number of ADHD cases in children and adults is really due to poor sleep with apnea being a major factor (http://www.webmd.com/sleep-disorders/sleep-apnea/news/200608...).