Hubert Selby Jr's Requiem for a Dream

I am here to ask a specific question about Selby's novel which would go onto be adapted into a critically acclaimed film by Darren Aronofsky. I am trying to place this book in a category as I like to put my books into different sects in order to allow me to find them quicker and compare with other books. Which of these shelves would the book go into? [Adapted], [ExtremeLit], [Drugs], or whatever you would suggest?