I am wondering why i get tired (as in nanna nap time) on ritalin whereas dex never had this effect on me. It is frustrating as i am grateful to be finally able to sleep at night with no problem but need to be able to study during the day. At the moment i am still increasing slowly on ritalin 10 but am definately bothered that on 3 dex every three hours i was fine but already on ritalin i get tired.
Feeling tired is a rather common side effect of stimulant medications (ironic, I know). Your best bet is to ensure you're getting regular exercise and enough sleep. You may also find that once your Ritalin dose is increased that tiredness will not manifest.
While amphetamine and methylphenidate are chemically very similar, they are not identical, and will effect different people in different ways.