Robert Downey Jr. plays a drug addict in the film. This proved prophetic, as he suffered drug and alcohol addiction in later life. He recalled: "Until that movie, I took my drugs after work and on the weekends. That changed on Corrupción en Beverly Hills (1987), the role was like the ghost of Christmas future. The character was an exaggeration of myself. Then things changed and, in some ways, I became an exaggeration of the character."
According to the "Robert Downey Jr Film Guide" website, Marek Kanievska suggested Robert Downey Jr. and Andrew McCarthy should go out and party to 'get into character' which ended with Downey in the middle of Santa Monica Boulevard, howling at the moon, and McCarthy had to bail him out of jail.
Despite the rough experience of the shoot, Robert Downey Jr. considers this movie to be one of his all time favorite movies of his own, citing his performance of Julian Wells as "the ghost of Christmas Future," to his personal life.
Because the novel didn't have a central plot or a core set of protagonists, but was more a set of interwoven events happening to a larger group of friends, this film differs considerably from the novel. In a surreal twist, the sequel novel, 'Imperial Bedrooms', has the original novel's characters aware of the film version of "Less Than Zero."
A test screening of 15 to 24-year-olds revealed that the sample disliked Robert Downey Jr.'s character. So, reshoots were conducted with additional footage to show his and Jami Gertz's characters in a better light which included the happy and celebratory early graduation sequence.
Brad Pitt: Uncredited, as an extra/background artist portraying a preppy guy party-goer and seen as Clay Easton enters the party at the movie's beginning.