Is it breaking the law? The
FDA has stopped the "marketing of quinine for non-approved uses" and the only approved usage is Malaria treatment. They've also stopped the sale within the USA of all brands except for one approved brand. However, if you buy it from somewhere else (a Canadian pharmacy for example) and had it delivered to the USA is it breaking the law?
The transaction happened elsewhere and the item isn't expressly prohibited (just can't be marketed and can't be sold within the USA).
I'd be interested to hear a lawyer's opinion, but just because something is having restrictions applied doesn't mean that importing it is illegal. Providing you're not breaking the law by purchasing it in a foreign country nor importing it (neither seem to be expressly illegal from what I can see).
Of course, I'm UK-based but your surely your government can't make up laws on the spot, so if it's not expressly denied then it shouldn't be illegal.
That said, I'm not saying it's advisable to take quinine sulfate for this purpose...just discussing the issue at hand.