Shots of Adrien Brody sobbing in the body drawer were real. Brody had asked director John Maybury to keep him locked in, even when they weren't filming, so he could get the feel of the character's despair. Eventually, Brody lost it during filming, and Maybury caught it.
Keira Knightley credits the food poisoning she had during her audition for landing her the part of a sickly alcoholic.
The film is based on the story "The Star Rover" by Jack London, which in turn, was based on his interviews with Ed Morrell, who, while in prison at San Quentin, was tortured, often with a very tight straitjacket, which constricted his chest, breathing, and blood flow. In order to cope with this, he quickly learned self-hypnosis, similar to what Jack Starks (Adrien Brody) goes through.
Adrien Brody did sessions in an isolation tank, performed prison exercises, and went on a protein diet for his role as war vet Jack Starks.
The scenes in the mental hospital were shot in the former Bangour Village Hospital, an unused insane asylum, in West Lothian, Scotland, near Edinburgh. As this movie was released, several other film scouts expressed an interest in the hospital building as a location, but the area had already been earmarked for housing development. Since then, the housing development has been scrapped, and Bangour Village Hospital still stands, as it did at the time of filming, and continues to attract ghost hunters, as certain patient villas are believed to be haunted. It is now a building site for a new village since 2019