(TMZ) - Amanda Bynes was arrested in Los Angeles yesterday after cops determined she was driving under the influence... and law enforcement sources say she was on drugs, TMZ has learned. One informed source says it's weed.

TMZ is reporting that Bynes was driving a Mercedes in the San Fernando Valley when she stopped in the middle of an intersection on Van Nuys Blvd.  

A CHP officer spotted her and determined she was under the influence.  She was taken to the LAPD Van Nuys division where a drug recognition officer evaluated her and determined she was under the influence of a drug.

Amanda was then booked for DUI.  She posted $15,000 bail.

Amanda has had trouble with mental problems for years now.  Her parents had a conservatorship which ended earlier this month and as one source says, "Things started going haywire."

TMZ reports Amanda has moved out of her parents home and is now living in an Orange County apartment, and that she has been smoking weed for weeks and things are bad again.

The arrest triggers a legal problem.  Amanda is on probation for a wet reckless conviction last February.


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