https://www.newyorker.com/magazine/2017/10/30/faces-of-an-ep... will give you some human form

Prescription opiates that lead to street drugs like heroin or illicitly-sourced ones after the prescription runs out, is my understanding. I don't know how the numbers break down in terms of initial exposure - how many bored desparate people were seeking a release, how many people got injured and then got hooked, etc...? But when we end up talking about drugs designed for 2,000lb elephants, it doesn't seem purely a problem of doctors/pharmacists, people are getting it from some unofficial sources.