It may be a myth, but it is a very popular one, that some vikings used fleinsopp (Psilocybe) to go berserk.
The following is for those who read exotic languages or trust AI to translate. The title suggests herbal intoxication, rather than mushrooms, though. The web site has a positive reputation, I think.
Here is an english language one that talks about the same paper. I remember reading it when it came out, which is why i know about henbane in beer...
Whether it involved Laudanum or not I cannot say, but Charlemagne ordered the planting of poppies (opium) for medicinal purposes 3 centuries before the crusades
Mostly.
After all, Ars Magica is set in an otherwise recognisable pastiche of medieval Europe.
I am beginning to realise my casual question is very dependent on the economics of supply and demand - both the supply of narcotics/inebriating substances is apparently expensive and/or dependent on where the raw materials can be grown and the difficulty of transporting them fresh. And the demand is presumably from people who can afford the luxury of neglecting what can be considered subsistence labour due to inebriated state.
Come to think of it, there would also be a social cost - being charged with "Sloth".
Perhaps, perhaps not. After all this is an era where priests openly visited brothels (In Italy at least) which were praised as being a safe outlet for men's lustful impulses. Travel for vacation was socially acceptable so long as you called it a pilgrimage, and excess work could be frowned upon as being a slave to greed. Most sins were not charges in any sort of formal sense, they simply imperiled your soul and brought social disapproval. Drunkards were certainly common enough, and any form of narcotic was easily explainable as being taken "for health". Hemp will certainly grow in Europe, but would be of low quality. Certainly nobody was cultivating high end strains like is done today, but hemp rope was certainly around, and I'm sure plenty of people "smoked string" (term from 19th century America and early 20th century) with nothing like the strength we associate with the modern day regulated drug.
IIRC, the romans did what I'm told most mediterraneans do today, and diluted wine with water.
... not when they sought the intoxication, I don't think
... and could afford it, if they had any say about their drink. Watered down wine was around the mediterranean often the substitute for clean water for the urban masses: slaves, workers, soldiers, mariners and such.
Ancient greeks, romans, and etruscans generally did dilute wine with water, just before the meal/party, in a big vase (called crater in Latin, from the greek ÎșÏ៱ÏÎźÏ),. Drinking wine undiluted was considered a form of boorish excess. If and when people started drinking undiluted wine (almost always this happened after starting with normal, diluted wine) it meant the party had gotten really out of hand.
But the notion that most mediterraneans today would dilute wine with water is pure slander!
Keep in mind that today during a meal one typically drinks wine, and separately water too. The ancients instead drank a single mix. Quenching one's thirst just with (undiluted) wine through a whole meal ... well, I've done it a few times, but not once could I have called myself even remotely sober at the end 
With apple cider (or american beers) it's certainly more doable
My apologies for (unwittingly) spreading slander.
I knew the romans drank diluted wine, and an italian person recently said something about "wine and water", but I have to admit my italian is very poor and so I must have just pattern-matched to known information.
Of curse there's also the question of why magi would bother with narcotics when you can do a range personal duration diameter PeMe for giving a $%#&.
In the books there's a flower that causes magi to warp. It's addictive and pleasant. It's called Amaranth.
The âspice roadâ also brought opium from the east, that the Muslims were using medicinally. Herb wives and folk healers dealt in herbal concoctions that could have powerful effects. Almost all âprimitiveâ cultures found by anthropologists have some intoxicants.
I would work under the assumption that drug use, in the form of ânatural Philosophaie,â the witch at the edge of the village, or other hedge traditions was known.
What is the difference between a medicine, a drug, and a poison? Dosage.
Opium also turns up in the Pentamerone (Italian).. THe sleeping draughts in Straparola are likely opium.