Most people say that Requiem for a Dream is the drug movie. I haven't actually seen it. I need to see some more David Lynch films sometime. I really liked Mulholland Dr., although there's a clear break about an hour and a half in, where the plot descends into total weirdness, and there's no symbolic explanation for anything that happens. The first part of the movie is great though, and it probably would have made an interesting series. You can tell that the first half was for TV since there's no swearing or nudity, but the rest of the movie has much more R rated content.