"my son is 13 years old and has have been on adderall for about 6 years now and was recently switched from adderall xr 15 mg to adderall xr 20 mg. today is his first on the 20 mg. so far he noticed a large difference in the effects. he said when he was on 15 mg xr for 2 years and he didn&#039;t even notice his attention span had dropped and his grades had also been, he said felt no effect whatsoever from 15 mg. the 20 mg has a noticably large increase in effectiveness . for the first time in months he feel back to normal and refreshed. he said never knew my body could grow a tolerance to a medication so quickly. i am curious if every dosage will get weak like the 15 mg. i don&#039;t want to keep elevating the strength for him as i&#039;m worried it is bad for his health."