People tend to view drug use as a lazy alternative to healthy living, but I think it might be better to flip it around and say that drug use (ranging all the way from caffeine and nicotine through to heroin and meth) is a symptom of something wrong. Schizophrenics, for example, are known to self-medicate with nicotine prior to their diagnosis.

I think it's important to remember the hidden underlying problem won't go away just because the visible coping mechanism does. A severely depressed person using modafinil as a crutch has to treat the depression first and foremost.