Depends on what you mean but I have never "cheated" if that involves any form of plagiarism (including copying other peoples work or illegitimately acquiring answers to tests etc).
I have and continue to experiment with all sorts of "smart drugs", including prescription-only ones like ritalin and modafinil, though. I guess it is "cheating" in a very abstract sense since I do have an unfair advantage in that I get more studying done with them than without them (and a lot, probably most, of people do not use them).