I used Adderall for Dustin for a while.
About
Adderall. (this is an online pharmacy but it has GREAT information)
The medication has a fast processing cycle but it isn't good to start and stop the med, he needs to be consistant with taking it. It is like getting on and off a roller coaster ride, that just isn't good when you are dealing with the brain!
Adderol made Dustin lose weight quite drastically, but he also has Cerebral Palsy so he has a VERY high calorie burn and was under weight to start with.
Give it a couple weeks, monitor how he is behaving, monitor his weight and record all of that. Then talk to the doctor if you do not see changes for the better in his behaviors and concentration, and if you see significant weight loss for his size and build.
Currently, Dustin is on Risperdal and Luvox. We have seen major improvements in his concentration, redirection from obsessive behaviors and other things. It took quite a while for us to find this combination of meds, but it took an awesome doctor from Hershey Medical Center to help us do this.
I hope your son is able to be helped with this medication.

What meds has your sons doctor tried with him?
Is this a doctor who specializes in treatment
of ADD and Pervasive Developmental Disorder?