Also, the demand from Oxy addicts created (or, I suppose, upgraded) a criminal network that supplies heroin. When I was growing up there weren't that many heroin addicts around, so the local independent pharmacies didn't stock it.

If you were an adventurous youth looking for a new high you would have been sold barbiturates, maybe, or benzodiazepines. Maybe speed. But today it would be heroin, and you can trace at least some of that back to oxy addicts desperate to feed their addiction after being cut off.