Less Than Zero received mixed reviews among critics. Ellis hated the film initially but his view of it has softened in recent years. However, he insists that the film bears no resemblance to his novel and felt that it was miscast with the exceptions of Downey and Spader.
During Clay's visit back home, his relationship with Blair rekindles and Julian's attitude becomes more volatile — he was forced by Rip to become a whore in order to sustain his fixes. After one extremely drug-fuelled night, Julian decides to quit, and starts to make up with his father. Later on, however, he is tempted back once again into the seedy life he was trying to leave. Blair decides to get clean, also, and Clay rescues Julian, and after a final face-off with Rip, they escape Los Angeles. The three drive through the night, with Julian relinquishing promises of going clean again. Sometime the next day, Clay pulls over to find that the sleeping Julian has actually died of an overdose. Clay and Blair are then seen after Julian's funeral, where Clay tells Blair about the death of Julian's mother and how it affected him. Clay then tells Blair he is going back east and wants her to go with him; she agrees. The final scene of the film shows the couple leaving town and then the picture of Blair, Clay and Julian at their graduation. This is the last time the three are seen happy together.
Also, in the book, Clay must decide whether he wants to continue his relationship with Blair, while in the movie they have already broken up and Blair is now involved with Julian. Though Blair called him while he was back east, Clay seems to have given up on both of them. It is after the scene when Clay is swimming that Clay appears to have decided to re-involve himself with Blair and Julian, while in the book he seems uncertain he wants to continue with her the whole time, even saying at one point that he never loved Blair. Also, in the film, Clay is determined to clean up Julian's drug abuse and debts, but in the book Julian's behavior only seems to disillusion Clay with the people in Los Angeles even more. In addition, many of the characters in the movie never existed in the book.
Other minor changes include: Clay and Julian are not blonde and tan like they were in the novel. Rip is Julian's dealer in the movie, when in the book Rip was Clay's dealer (Clay was a frequent drug user in the book) and Julian is a dealer himself but is also indebted to a dealer named Finn; in the book, Clay goes both ways sexually and romantically, while in the movie, he's strictly hetero, and Clay's friend Trent, who was a major character in the novel, has a greatly reduced role in the movie.
Many important, plot-bearing scenes from the book were also removed in the translation to film. These removals are arguably the most obvious strays from Easton Ellis' novel. Of these are: a very profound scene describing in great detail (to show the importance, contrary to the rest of the novel's loose details) Clay and Blair running over a coyote and Clay seeing it die; a scene where Clay and friends see a dead body in an alley, which helped show how exposed to the world the teenagers were at such a young age; and the famous final scene where a 12-year-old girl is tied to a bed and raped in Rip's apartment.
20th Century Fox then assigned the film to producer Jon Avnet who had made Risky Business. He felt that Cristofer's script was "so depressing and degrading." Avnet instead wanted to transform "a very extreme situation" into "a sentimental story about warmth, caring and tenderness in an atmosphere hostile to those kinds of emotions." Studio executives and Avnet argued over the amount of decadence depicted in the film that would not alienate audiences. Larry Gordon, President of Fox, and who had approved the purchase of the book, was replaced by Alan Horn who was then replaced by Leonard Goldberg. Goldberg found the material distasteful but Barry Diller, the Chairman of Fox, wanted to make the film.
Harley Peyton was hired to write the script and completed three drafts. In his version, Clay is no longer amoral or passive. The studio still considered the material edgy and kept the budget under $8 million. Marek Kanievska was hired to direct because he had dealt with ambivalent sexuality and made unlikeable characters appealing in his previous film, Another Country. The studio wanted to appeal to actor Andrew McCarthy's teenage girl fans without alienating an older audience.
At an early test screening, the studio recruited an audience between the ages of 15 and 24; they hated Robert Downey Jr.'s character. As a result, new scenes were shot to make his and Jami Gertz's character more repentant. For example, a high school graduation scene was shot to lighten the mood by showing the three main characters as good friends during better times.
The film has had mixed reviews among critics. It currently has a rating of 63% on Rotten Tomatoes. In the New York Times, Janet Maslin wrote, "Mr. Downey gives a performance that is desperate moving, with the kind of emotion that comes as a real surprise in these surroundings. Rita Kempley, in her review for the Washington Post, called the film, "noodle-headed and faint-hearted, a shallow swipe at a serious problem, with a happily-ever-after ending yet. In Newsweek, David Ansen wrote, "Imagine Antonioni making a high-school public-service movie and you'll have an inkling of the movie's high-toned silliness. In the Chicago Sun-Times, Roger Ebert gave Less Than Zero a four-star review, noting that the "movie knows cocaine inside out and paints a portrait of drug addiction that is all the more harrowing because it takes place in the Beverly Hills fast lane . . . The movie's three central performances are flawless . . . [Robert Downey Jr's] acting here is so real, so subtle and so observant that it's scary . . . The whole movie looks brilliantly superficial, and so Downey's predicament is all the more poignant: He is surrounded by all of this, he is in it and of it, and he cannot have it".
Upon its initial release, Ellis hated the film but has gotten very sentimental about it in recent years. He admits that the film bears no resemblance to his novel but that it captured, "a certain youth culture during that decade that no other movie caught," and felt that it was miscast with the exceptions of Downey and James Spader. The film was voted as the 22nd best film set in Los Angeles in the last 25 years by a group of Los Angeles Times writers and editors with two criteria: "The movie had to communicate some inherent truth about the L.A. experience, and only one film per director was allowed on the list".
The Red Hot Chili Peppers were featured in a scene of this movie, playing "Fight Like A Brave".