Yes it is a Southeast Bias [1]. Check the map and choose the lowest IDH regions. and google it.

and "For some other kinds of medication, it's probably true that people get them from the black market (think benzos)."

Please, the market does not care what kind of medicine is dealt with, the black market is there to provide anything. You just need to go to the country side to see it.

[1] - https://en.wikipedia.org/wiki/List_of_Brazilian_federative_u...