From the movie Drugstore Cowboy,
Quote:
Bob: Most people don't know how they're gonna feel from one moment to the next. But a dope fiend has a pretty good idea. All you gotta do is look at the labels on the little bottles.
Without the drugz (legal or illegal) your choice is stay depressed, not sleep, not wake up, not have sex, etc. Not that popping pills like Elvis is a healthy or a good idea, but people take them because it gives them an option that they otherwise don't have (and which humans haven't had for most of history). Like people drinking coffee at work to increase energy and motivation.