Forensic pathologist Dr. Cyril Wecht is talking to ET about the dangers of mixing certain medications -- and how they can affect one's body.

Watch the video to hear Dr. Wecht describe how certain prescription drugs, if present in one's system at the same time, can "act faster than it takes me to describe orally, and then you have cardio-respiratory depression and death."

Wecht, who consulted on high profile cases like the deaths of Anna Nicole Smith and her son Daniel, tells ET: "It's a painless death, but one that ironically does not permit you to cry out for help because you have no pain, you have no agony…."