don't know about ritalin, but adderall is instant (well 30 minutes).
== == == == I'm not 100% sure, but I think it's because they become drier. Yes, this is because they get dried out and also because of the blood pressure in the eye. If you work on the computer all day simple eye excercises can prevent this. It is caused by dryness. Try using systane ultra drops 2xday.