The 28-year-old 'She's The Man' star, who seemed to be turning her life around after coming out of a near six-month stay at a rehabilitation clinic late last year, was on a "stimulant" at the time of her arrest, according to TMZ.
While driving her Mercedes in the San Fernando Valley, Bynes was stopped on Van Nuys Boulevard in the middle of the intersection by a California Highway Patrol officer.
Shortly after, she was transported to the local precinct where a drug recognition officer came to the conclusion that she was under the influence of some kind of drug.
"As far as the criminal case is concerned, she is facing the real possibility of jail time," criminal defence attorney Troy Slaten said.
"If she is convicted of a second-offence DUI, the law requires a minimum of 96 hours (or four days) of jail.