you know I have views about this but I feel you should put this question onto the ADD and ADHD Doctor forum, look at the top of the forums ,on the right, there is a Dr Resnik who is very good at answering these kind of questions about meds, my laymans/ parent answer is to wean him off them and try the supplemnts that have been shown to work, however you need your Doctors advice getting him off them.
PS Read the thread below there is good information there aswell ,