EXCLUSIVE

Toxicology testing shows Scott Weiland died from an overdose of several drugs and alcohol -- and his history of addiction also played a role.

The Hennepin County Medical Examiner says the results show he OD'd on cocaine, MDA ... which is old school Ecstasy ... and booze.

It also shows heart disease and asthma were "significant" conditions. The test results also revealed Scott's "multi-substance dependence" was a factor.

As we first reported ... police also found Xanax, sleeping pills, Viagra, and meds to treat bipolar disorder on the bus -- but those drugs did not play a factor in his death.