Vincent D'Onofrio purposefully mouth breathed during the entire production to create a unique timber and respective speech patterns. He then added a "nose squeak" after finding that some persons who lost their nose secondary to trauma or cancer produce a high pitch sound after completing certain sounds.
Vincent D'Onofrio purposefully developed a bad and uneven suntan, gained a significant amount of weight, bleached his hair, and wore improperly fitting skateboard apparel. When he reported to the set, he arrived in character.
Warner Brothers was not comfortable with the significant drug content and the John F. Kennedy assassination sequence, and initially wanted an edited version of the film for a wide theatrical release. The scenes remained, but the film then was only given a limited theatrical release.
Val Kilmer researched his role by spending time with drug abusers in Riverside and the greater Los Angeles area.
Writer Tony Gayton said that the script to this movie was not written to be produced but to be a writing sample, something wild and experimental he could show producers to get work. He was very surprised when Castle Rock wanted to produce it.
In order to prepare for his role, Doug Hutchison spent a month with real narcotics officers and accompanied them on drug busts.
Val Kilmer spent up to three hours a day in the makeup chair for placement of numerous fake tattoos on his arms, chest, and back.
Peter Sarsgaard grew in a mullet over a three month period for the film. During this time he also went to crystal meth anonymous meetings and various juvenile halls.
Peter Sarsgaard's character is based on a real person who was a meth user in Riverside and according to D.J. Caruso "Just wanted to be liked".
Deborah Kara Unger researched her role in the film as a drug user by visiting the Riverside Recovery Center.
Although screenwriter Tony Gayton did not expect to sell the script, it ended up selling in three days after Gayton's agent David Saunders (APA) sent the script to original producer Ken Aguado.
Val Kilmer wrote of his audition for Stanley Kubrick's Full Metal Jacket (1987). The role eventually went to Matthew Modine. In this film, Kilmer co-stars with two major actors in that film, R. Lee Ermey and Vincent D'Onofrio.
Val Kilmer and Peter Sarsgaard both appeared as characters in DC universe movies, Kilmer as Batman in Batman Forever (1995) and Sarsgaard as one of the villains in Green Lantern (2011).