"That '70s Show" actress Lisa Robin Kelly died from "multiple drug intoxication" ... and the L.A. County Coroner tells TMZ her death has been ruled an accidental overdose.
TMZ broke the story ... Kelly -- who played Eric Forman's older sister on the show -- died August 15th at an alcohol rehab facility in L.A. County.
An autopsy performed immediately after she died failed to identify the exact cause of death -- the coroner had to wait until the toxicology results were in.
The coroner did not identify which drugs were in her system.
Just days before her death, Kelly had been hospitalized with an alarmingly high .34 blood alcohol level ... a level that can sometimes lead to death.
The Coroner's full report will be released within 2 weeks.