08/18/2013 at 12:00 PM EDT
An autopsy on Lisa Robin Kelly was completed Saturday, but the cause of her death will not be known for at least another two months.
It will take that long for toxicology results to come back from the lab for the That '70s Show
star, a coroner's office spokeswoman tells CNN
Kelly died in her sleep
Wednesday night after voluntarily checking herself into a treatment facility earlier in the week to confront "the addiction problems that have plagued her these past few years," her agent, Craig Wyckoff, told PEOPLE on Thursday.
"I spoke to her on Monday, and she was hopeful and confident, looking forward to putting this part of her life behind her," he added.
According to TMZ, the actress, who made her TV debut on Married... with Children
in 1992, had been arrested at least four times over the past three years for DUI, spousal abuse and assault.