Former drug addict Robert Downey Jr drew on his grim experience for movie A Scanner Darkly.
The 41-year-old who has a well-publicised history of drug problems and has spent time in jail for possession, knows well enough about the kind of people involved in the dark world of substance abuse who appear in director Richard Linklater's animated film.
Yet he says his past came in to play for the movie: "Watching the movie, it was kind of funny how my character's paranoid can-I-trust-my-buddies references were so sick and so fun to see."
The Charlie Chaplin star had hoped he could exorcise his demons by taking on the role in Philip K Dick's story about an LA cop (Keanu Reeves) investigating a drugs den.
But he said the reality was a little different: "It wasn't a cathartic or luminous thing for me because the movie is about a drug-addled society."
A Scanner Darkly - also starring animated incarnations of Keanu Reeves and Winona Ryder - is out on August 18.