"There is a strong selection bias among the people I see" This is a real problem in drug policy. The majority of drug users stay well clear of medical professionals. They learn quickly not to discuss their habits with doctors or nurses as it leads all sorts of problems.

Prescription pain pills are not heroin. They are dangerous in overdoes because of the effect they have on the breathing reflex. It is a common practice among the drug addicts I knew to never let a fellow user 'nod off', that is loose consciousness as it leads to death when they stop breathing.

This is not a problem for heroin addicts using heroin. But (in the world I inhabited 15 years ago) heroin was very rare.