Heather Locklear   has been formally charged with driving under the influence of drugs in connection with her   September arrest, the Santa Barbara, Calif., District Attorney's Office said Monday.  

The misdemeanor charge filed by the DA's office specifies that the drugs in question were "prescription medications." If convicted, the actress, 47, faces penalties ranging from a fine to up to six months in county jail.  

An arraignment was set for Jan. 26 in Santa Barbara Superior Court.  

"Lab tests showed she had no alcohol in her system and no illegal narcotics of any kind," says Senior Deputy District Attorney Lee Carter, who declined to comment on what medications – or the amounts – Locklear had taken.  

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

Locklear was originally booked on charges of driving under the influence of drugs and being under the influence of a controlled substance. The latter charge was not filed because, says Carter, "There were no illegal substances in her system."  

In addition, felony charges for Locklear "were not a possibility," because DUI cases with no injuries are always misdemeanors, he said.  

The former   Melrose Place   star was arrested Sept. 27 in Montecito after an eyewitness – who turned out to be a paparazzo – called 911, saying Locklear was "driving erratically."  

In July, Locklear completed four weeks of treatment for   anxiety and depression.  

Locklear's attorney and publicist both declined comment.
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