I think it's like that most everywhere (at the very least, in the US) not just the rural South. I can't remember who sent it, but there was a great tweet I read once that went something like:

"The two biggest surprises of my transition from childhood to adult life were learning that:

1. Everyone is on cocaine. 2. Cheese is fucking expensive."

And sure enough, as I approach 40, practically every adult I know regularly uses at least one—and usually several—mood-, mind-, or perception-altering drugs, legal or otherwise. I'm sure it was true when I was a kid, too, but a combination of my own obliviousness and DARE programs had me thinking otherwise.

[EDIT] actually, I bet it's like that everywhere, period, with few exceptions. There was a travel photo-blogger I used to read a lot, and a common feature of trips to relatively remote and non-touristy/low-development areas was "here's the stall where they sell the one or two obscure-to-westerners drugs that every single adult here takes every single day" For developed areas I expect that only didn't happen because, outside of tobacco, alcohol, caffeine, maybe weed (quite a list already!), plus, you know, drug stores full of prescription drugs, the drugs aren't sold openly like that.