Many of the replies on this thread are pretty good evidence that you can apply to med school and still not have a clue. Ritalin, Aderal, crystal meth, whatever, will not necessarily send you into a violent tizzy, fry your brain (what does that mean, actually?), or make you go to hell. If taken when it's not appropriate, they can be risky, and there are probably going to be adverse effects on even the best of days. Also, they may not have the effect you want. And none constitutes intelligence-in-a-bottle. But:
In some people, some drugs (notably the two you mention) can increase the ability to concentrate in some people. End of story about efficacy.
In some people, these and nearly every other drug can do bad things, sometimes (rarely, if your dosage is sensible and you don't make a habit of it) real bad. End of story about medical drawbackks; get details before you decide.
Assessment of legal risks for possessing a controlled substance, and moral consequences, are best left to the individual.
If you want to risk it (including the whole legal issue, and that going to hell thing), just be sure to try it on a practice exam or two, well before the real deal. Don't do anything on exam day if you've never done it before.
Now excuse me, I have a shipment of PCP to sign for.
(OK, the inevitable disclaimer: I am not advising anyone to take any medication without the advice and consent of the Sena. . . [oops, wrong professional school]. I have not done so, and don't know whether I would even if I thought it would help. I happen to take Ritalin; ask the shrink who prescribed it whether he thinks it's appropriate.)