Adderall XR Dosing | ADHD Information

My son is 11 and is currently on 50mg of Adderall XR.  I know this isn't based on weight or size, and the Dr. said that he wouldn't put him on a higher dose, he would change medications if this doesn't work.  He has been on this medication for three years and worked up to this dose.  The doctor added Clonidine for impulsivity and he is doing much better.  In the past we have tried Concerta, Strattera, Metadate, and Ritalyn.  Concerta worked for several years and then we got to 72 mg and decided to change to the Adderall.  I am curious about what doses of Adderall XR other people are on.  Also, what are our other options.  Has anyone ever gone back to a previous med that quit working and it was successful again?  We have tried the weekends with half the Adderall dose and it is ok if we aren't going anywhere, but if we do it is a nightmare.  My son is on 25 mg...I believe that giving him some med breaks helps with not having to increase the dose quite as often ( I plan to use the spring break for a medication break). The doc initially prescribe him 30 mgs but I decreased the dose and he seemed to do fine on 20mg.    Just a few weeks ago we had to increase to the 25.  ( BTW my son is 7 almost 8 years old)