01/03/2014 at 05:00 PM EST
Almost six months after Lisa Robin Kelly passed away in her sleep
, her cause of death has finally been revealed.
The actress, 43, best known for playing Eric Forman's sister on That '70s Show
, died from multiple drug intoxication, PEOPLE has confirmed.
The L.A. County Coroner has ruled the death to be an accident.
The specific drugs in Kelly's system were not noted, but she had a history with illegal substances and was arrested at least four times over the past three years for DUI, spousal abuse and assault.
At the time she passed away, Kelly's agent Craig Wyckoff told PEOPLE
she had "addiction problems that have plagued her these past few years." In fact, she had voluntarily checked herself into a treatment facility earlier in the week, Wyckoff said.
was the first to report this story.