'Real World' Star Ryan Knight -- Death Ruled Accidental OD

"Real World" star Ryan Knight's death was caused by a deadly mix of multiple drugs and alcohol according to the final autopsy report.

The Kenosha County medical examiner concluded Knight had various drugs in his system, including methadone (a heroin substitute), tramadol (a painkiller), cocaine and Xanax -- mixed with a high level of alcohol.

The medical examiner ruled the death an accidental overdose.

TMZ broke the story ... Knight was found dead and covered in his own vomit in November, after partying hard in Kenosha, WI.

Knight was 29 years old.