Concerning illegal opioids (like fentanyl)

Opioid Crisis 

Premise: concerning illegal opioids (like fentanyl) 

The increased accessibility of potent synthetic opioids like fentanyl contributes to the rise in overdose deaths (50 and 5000 times as powerful as heroin, respectively). Very high overdose risk is linked to the misuse of these medicines or unintentional exposure to them (for example, when they are laced with heroin), and naloxone doses that could reverse prescription-opioid or heroin overdoses may not work. Overdoses must be prevented, detected, and reversed using new and better methods.

Question: With this, who’s to blame here? how might we work to tie this in more directly — if the opioid epidemic began with people being prescribed these legally (although excessively), where/how does illegal acquisition here fit in? I can see how this creates a kind of cycle of addiction , but again,  where/how I can make that fit in a bit more clearly.