Perhaps. I'll bet the figure was much lower during Prohibition.
I would guess the same. Which leads one to conclude that removing prohibition (criminalization) would increase the number of users, thereby forcing the hardcore abusers back into a minority.
Correct me if I'm wrong, but wasn't it you who said that drug use wouldn't increase with legalization? That those who want to do drugs are doing them today? The mere legalization will not "cause" people to suddenly take up drugs?