It's also worth watching episode 7 of Anthony Bourdain's Parts Unknown where he goes back home to Massachusetts. A large portion of the episode is focused on this.

You have kids in high school who are injured in sports, are prescribed painkillers by their doctors which eventually gets them on heroin. The addicts didn't wake up one day thinking, "You know what? I think I'm going to try heroin today." It was legal pharmaceuticals with falsely advertised addiction rates that got them onto it.