In your opinion, what are the best "druggie" movies?

By druggie movie I mean something that is serious, nothing like Dude, Where’s my Car?, Block Party, Friday, The Cheech and Chong series, or Rolling Kansas (Even though they were great). I’m talking about A Scanner Darkly, Requiem for a Dream, True Romance, Spun, Brick, and Blow. I think you get what I mean, they have to be serious, and the main focus has to be on drugs, not just one point in the movie where some guy snorts a line.