New data have been published on drug overdose deaths in 2020. Although you won't find it anywhere obvious, prescription opioid analgesics remain only a minor (and stable) contributor to the record 93,000 people who died from drug overdoses last year.
Dr. Singh, ACSH friend and former Chief Medical Officer for the Office of the Assistant Secretary for HHS, published a paper on the adulterants found in street drugs. What was in there? A lot of junk.
There are many good reasons to avoid illegal drugs, like addiction and overdosing. The next best is that local street chemists aren't terribly trustworthy. It's common for drugs to be mixed with other chemicals, some of which are far more dangerous than the drug itself. Case in point: Fentanyl, which is often mixed into heroin.