Los Angeles County Superior Court Judge Edward Moreton on Tuesday referred the case to the court's mental health division, where a judge will decide if Bynes is fit for trial, the court said.
Her drunk driving case stems from an April 2012 incident in which she was charged with driving under the influence in West Hollywood. She was arrested on suspicion of DUI after she allegedly clipped a sheriff's deputy's cruiser while trying to pass it around 3 a.m. near Robertson and Santa Monica boulevards.
Police said Bynes refused to take a sobriety test.
She pleaded not guilty last year to the driving under the influence charge. Her next court date is scheduled for Jan 7.
She is already on probation in California for driving on a suspended license, and faces charges in New York for marijuana possession and throwing a glass bong out of her 36th-floor Manhattan apartment.
Bynes, who starred in her own sketch comedy TV series "The Amanda Show" at age 13, has become as famous for her erratic behavior, brushes with the law and odd postings on Twitter as she has been for acting.
Last month her mother, Lynn Bynes, was granted temporary control of her legal and financial affairs while she undergoes psychiatric treatment.
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