I drink caffeine (tea usually, and also usually not after 4pm) but I don't think it enhances my intelligence.
This touches on something that I was going to ask about. By "increase academic performance", which of these are we referring to?
a) productivity enhancers - allowing students to stay awake for longer periods of time, thus having more time to digest the material
b) drugs to actually increase intelligence/reasoning ability/speed of cognition temporarily (excuse the fuzzy definitions)
Clearly
a) is possible - caffeine has long been used to cram for tests and finish assignments on time.... by some students

, and as this New Yorker article suggests
http://tinyurl.com/cm4b75, certain classes of amphetamines are now commonly being employed for this purpose at top US colleges.
I am curious, though, whether there is any drug that can accomplish goal
b). My own experiences completely agree with Eriny's: taking NoDoz, for instance, allowed me to stay awake, but I feel that I actually performed worse at certain tasks (verbal fluency in LOTEs, for instance.) However, as humph notes, Paul Erdos believed that the use of amphetamines actually augmented his mathematical skils - it didn't just buy him more time to churn out proofs or whatever. The New Yorker article above also mentions some drug - modafinil I think it was - that seems to accomplish both ends; Wiki classes amphetamines as both productivity enhancers and "[improvers] of cognitive performance."
http://tinyurl.com/fgq2w The anecdotal evidence posted here seems to suggest that drugs such as caffeine work only as productivity enhancers.
Sorry for the rambling, but I thought it was necessary to draw a distinction here.