Production notes

The film was shot in North Carolina. The YMCA Blue Ridge Assembly in Black Mountain, North Carolina, served as the Serenity Glen rehabilitation center.

The film opened at number two at the United States box office making $10,310,672 in its opening weekend in 2,523 screens, behind Rules of Engagement, which was on its second consecutive week at the top spot. The film went on to make $37,035,515 in the U.S. The film made a total of $25,163,430 internationally, bringing its worldwide total to $62,198,945.

On Rotten Tomatoes, the film has a 33% approval rating based on 86 reviews with an average rating of 4.9/10. The website's consensus states: "Even though 28 Days is tackling a difficult subject, it comes off light and superficial, and maybe even a little preachy." On Metacritic, it has a score of 46% based on reviews from 26 critics, indicating "mixed or average" reviews. Audiences surveyed by CinemaScore gave the film a grade "B+" on the scale of A to F. Peter Travers of Rolling Stone gave it a positive review and wrote: "Count this rehab a success." Roger Ebert of the Chicago Sun-Times wrote: "Bullock brings a kind of ground-level vulnerability to 28 Days that doesn't make her into a victim but simply into one more suitable case for treatment." Owen Gleiberman of Entertainment Weekly gave the film a "B", stating that "Bullock gives it her all; she's bristling and alive on screen in a way that she hasn't been since Speed." Stephen Holden of The New York Times said it "begins with such a flurry of promise that it comes as a sharp disappointment when this drug-rehab comedy skids out of control." Kenneth Turan of the Los Angeles Times called it "Too glib too often to make much of an impression any way you look at it."