I am on 15mg of Adderall XR. I been off and on it since I was 15. I always was ok, focused, relaxed and ready for whatever work threw at me. But, yes the proverbial "but", it's not lasting 12 hours like it used to. I take it around 10am, start work at 1pm. By 4ish, my leg starts to shake. My mind seems to accelerate again, at top speed. All the hallmarks of ADD seem to return and I'm not even done work. Is it tolerance? Is it the pill itself? (since there is a shortage of the drug I take a different generic form of it from a different manufacturer) Any ideas before I tell my dr to increase?