Mischa Barton — the formerly willowy star of "The O.C." — was taken away by police and hospitalized under California's involuntary psychiatric-hold law just hours before she was due to fly to New York for the premiere of her movie, "Homecoming."

Cops took her to Cedars-Sinai Medical Center, where she was hospitalized under Section 5150 of the California Welfare & Institutions Code, which allows authorities to hold a person for up to 72 hours if they present a danger to themselves or to others.

Barton, 23, looked bloated and almost unrecognizable at a public appearance last week, which her reps blamed on the removal of a wisdom tooth.

PHOTOS: Click here for photos of Mischa Barton.

The once-scary-skinny starlet was arrested for DUI and marijuana possession in LA after driving in two lanes during a break from the movie's location work in Pittsburgh last year. She later checked into rehab.

Page Six reported that Barton would attend the premiere after we'd been assured by publicist R. Couri Hay that producers "Bingo [Gubelmann] and Austin [Stark] are hand-holding her from 4:30 to the premiere and through to the after-party at Pink Elephant, as she realizes the film is important to her."

RELATED: Psychiatrist: Mischa Barton Hospitalized, 'at the Brink of Disaster'

Stark said, "She was really professional and worked hard. It's a shame she can't come out and promote the movie. She did a great job."

Barton's publicist told People, "Police were involved due to Ms. Barton's celebrity status to safely transfer her to medical treatment as per doctor's orders." The rep said Barton was now "OK" and "resting."

RELATED: Click here for the full report from the New York Post.