California police investigating Heather Locklear's weekend arrest for driving under the influence (DUI) believe the actress was high on prescription drugs at the time of her arrest.

The former Melrose Place star was taken into custody by police in Santa Barbara after a local reported her "driving erratically" upon leaving a parking lot in the coastal city.

She was booked for DUI and being under the influence of a controlled substance, and held behind bars overnight before being released on Sunday (28Sep08) without posting bail.

Explaining the incidents leading up to Locklear's arrest, California Highway Patrol spokesperson Tom Marshall tells People.com, "Around 4:30 pm, a female witness saw Heather Locklear driving erratically while leaving a parking lot in Montecito. The witness said Locklear was revving her engine loudly, and backed over a pair of sunglasses several times. The witness called 911 because she was concerned for Locklear's safety. When a CHP officer arrived, Locklear was found seated inside her vehicle, which was partially blocking the roadway."

Authorities have ruled out alcohol intoxication after Locklear underwent tests at a local CHP station. Marshall adds, "Alcohol was ruled out as a factor, but based on the officer's observations, we believe Locklear was under the influence of prescription medication."

The news comes just two months after Locklear checked out of an Arizona rehab clinic, where she received treatment for anxiety and depression. (MT/WNWCPL/ZN)

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