Heather Locklear has been formally charged with driving under the influence of drugs (DUI).

The misdemeanour charge states the drugs in question are "prescription medications" and relates to the former 'Melrose Place' actress' September arrest, which saw her stopped in Barbara County, California, after she was seen driving erratically.

Senior Deputy District Attorney Lee Carter said: "Lab tests showed she had no alcohol in her system and no illegal narcotics of any kind. We believe the prescriptions she was taking could have impaired her ability to drive a motor vehicle safely."

If convicted, Locklear — who checked herself into an Arizona treatment facility in June to seek treatment for "anxiety and depression" — could receive a fine or up to six months in prison.

At the time of her arrest, officers with the California Highway Patrol claimed she showed "obvious impairment".

A witness called police claiming Locklear had been seen "driving erratically" and her parked car was then found blocking one lane of a highway.

An arraignment has been set for 26 January at the Santa Barbara Superior Court.

The 47-year-old star was originally booked on charges on driving under the influence of drugs and being under the influence of a controlled substance.

However, the second charge was dropped when tests showed no illegal drugs in her system.