It's a stupid drug to abuse.
It doesn't have all that much of an effect, at least in my experience, but if you take it a lot, you'll find that it's a very addictive drug. People get dependent on it quickly, and it's very hard to concentrate on anything unless they continue to take more and up their dosage.
Really not worth it imo. Do you really want to spend a year or two not able to concentrate on a damned thing, trying to become independent of a drug you didn't even need to take, just so you could make studying a bit easier during exam time?