Be careful. A lot of the drugs with strong effects necessarily have long term consequences from repeated use owing to their mechanisms of action. You risk making yourself 'dumber' over time with prolonged use. Especially, with the amphetamine based crap that US doctors seem okay to use for medical purposes despite most of the developed world not doing so, and using safer alternatives.
Out of curiosity, have you heard of any negative long term side effects from Modafinil and it's derivatives? (I don't think they are based on 'amphetamine')
The major concern with Modafinil is that we just don't know what the long term side effects are. That's the risk you take.