Uhh, no thanks. They werent exactly cutting cocaine, making crack, growing marijuana, etc. etc. in Medieval times. (Maybe Marijuana, and Poppy plants, but not for the reasons they are grown today) I didnt get skyrim to watch my character get high.

They have been growing and processing moon sugar grass for thousands of years. As well as refining that moon sugar to skooma.
So you're point regarding medieval times is actually nullified by Elder Scrolls lore.
(Other than that. Recreational use of opium, marijuana, coca leaves, quat, mushrooms, frogs, etc, etc, goes back millennia, much much much before medieval times.)