'Can't Buy Me Love' Star Amanda Peterson -- Cause of Death ... Massive Overdose

Amanda Peterson -- who starred in "Can't Buy Me Love" died from an accidental overdose of a deadly combination of drugs.

The 43-year-old disappeared just before the 4th of July and her body was found on July 5th.

According to the Weld County Coroner in Colorado, Peterson had a variety of prescription drugs in her system, including benzodizepines (anti-anxiety meds), opiates and phenothiazines (an anti-psychotic medication). She also had marijuana in her system.

One of the drugs in her system -- Gabapentin -- was prescribed for pain and the medical examiner said she had 6 times the normal level in her system.

The report says Peterson was "naive to opiates."

The toxicology report says a week before her death she told someone she ingested morphine medication she got from friends. The reports says she was self-medicating to control pain.

As for why she died, the report says it was because of a "morphine effect" ... which causes respiratory failure.