They say parents should choose a substitute carefully because the effects of these medications can vary widely.
For example, doctors say generics sometimes don't absorb into the bloodstream as easily and that can make it harder to get an exact dose match between medications.
If the dose is too high, sometimes kids can get more withdrawn or weepy. If it is too low they can't get adequate control of their symptoms during the day. That could cause a rebound later in the day.
Experts say, if you can't find any pharmacy that has the medication you need, let your child's doctor know. And, first, try a medication in the same class of medicines.