I'm a student of biology and upon getting my discharge summary I just did some research on the tests to understand what they meant, and the tests have healthy ranges on them. It's entirely possible this isn't from ethylphenidate, but it WAS what I was using prior to being admitted. It could also just be individual sensitivity to it, who knows, research chemicals and all that. Just to ease your mind, why don't you go to the doctor and ask to get a blood and urine workup - liver and kidney function tests can be done from that. Shouldn't cost you too much at all, in Australia I think it cost me $30, UK is probably quite cheap as well but the US might be more expensive but it will tell us what the effects of long term use are.