Hi hisnana,   Sometimes it can take quite a while to find the right medication and the right dose to be effective in both children and adults with ADHD. Some children require very small doses; some need higher doses. Same with adults- it is not related to ones weight. One med may work for one person, but not another. It really is a matter of trial and error until the right med is found and little or no side effects occur.   If your son has been on this regime for a few weeks and you've seen no difference, it is time to discuss this with his doctor to see if he needs an increase in dose or a change in medication.   Terry