Heather Locklear has been formally charged with a DUI, in connection with her September arrest. The misdemeanor charge specifies that the drugs in question were "prescription medications."

"Lab tests showed she had no alcohol in her system and no illegal narcotics of any kind," said the DA, but he wouldn't say what kinds of medications, or how much, were found.

"We believe that the prescriptions she was taking could have impaired her ability to drive a motor vehicle safely."

If the actress is convicted, she could get up to six months in jail. Her arraignment is set for Jan 26.