I don't think that's a widespread problem when it comes to antibiotics. For some other kinds of medication, it's probably true that people get them from the black market (think benzos). But antibiotics? Really? Do you know anyone who has ever done that? I'm sure those places exist but to say they are affecting resistance is a very big claim. And it has nothing to do with social class, every pharmacy I've been to in Brazil has been similarly paranoid about prescriptions, regardless of the neighborhood or clientele. Maybe that's a Southeast bias, but I'd like to see some hard data about black market antibiotics being so common.
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.
