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Peterson had apparently used a friend's medication for pain a week before her death, The Greeley Tribune reported.

Peterson had been prescribed multiple medications for lung and heart disease. She was also prescribed Gabapentin for postsurgical pain, but there were no recent prescriptions for morphine in her medical history.

The forensic pathologist and coroner both confirmed that Peterson died from respiratory depression caused by an overdose of morphine. The medication caused hypoventilation, resulting in a buildup of carbon dioxide in her body as her breathing became less frequent.

"The amount of morphine she ingested, coupled with her heart and lung disease resulted in a fatal event," coroner Mark Ward told the Tribune.

Peterson was found dead July 5 in her home after police responded to a well-being call. She had missed an appointment.

She was best known for 1987's "Can't Buy Me Love," a comedy in which she starred opposite Patrick Dempsey.