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The former OC star, 22, was also fined £837 and ordered to attend a three-month alcohol education programme after pleading no contest at a Beverly Hills court.
It was reported earlier this week that lawyer Anthony Salerno had secured a plea deal for the star, which included her marijuana possession charge being dismissed.
He said in a statement: "She understands the seriousness of this situation and assumes full responsibility for her actions."
Barton was charged with DUI, possession of marijuana and driving without a valid licence after she was spotted driving erratically in West Hollywood last December.
She did not attend the hearing.
