If you have anxiety problems you probably do not want to take a stimulant like Ritalin. Usually a stimulant will stimulate your anxiety and can actually make it more difficult to focus. If you really have major problems focusing in class and that sort of thing to degree that you feel it is significantly impacting your learning and grades, then you may want to talk to a doctor about the possibility of taking an anti-anxiety medication along with an ADD medication (all stimulants except Strattera which has very low efficacy). Of course, the best is getting by just fine without taking anything. But to answer your question, stimulants and anxiety problems tend to be a bad combination.