Did people in medieval times EVEN HAVE recreational drugs, I thought they were always too busy getting ruled over by fancy guys in castles and contracting the plague.
Europe produced a lot more wine in the middle ages then it does now; it was common to drink a mixture of water and wine for breakfast, with a "normal" daily dose of 1 to 2 liters, or 2-4 pints, per day for a man. The wine was drink with water and spices normally. Apple cider and similar stuff came around a bit later, and was sold to workers and miners.
There were several reasons for this love of wine: a) adding wine to water was thought to be healthy and probably did help disinfect stuff a little; b) the Christian "bread and wine" motif apparently had a part in ending the dark age, and also the monks (who had copied and thus preserved roman writings for centuries) knew that the Romans, the guys who'd built all those temples and rules over all of Europe centuries before, had had bread and wine -> being into wine was the fashionable thing to do for recently converted Christians.
Thus bread (which requires a miller, and an oven, and some infrastructure) replaced "boiled grains" as the main foodstuff when the middle age set in, and people wanted to drink wine, partly for religious reasons.
As for other drugs ... much of the European "herb lore" has been lost apparently, though there are some psychoactive substances around. It was highly dangerous being a healer though: Medieaeval people assumed that God controls anything that happens, including of course disease and accidents. Meddling with God's will by curing the dying? Burn him! (AFAIK more people were killed for having attempted to cure someone than for having attempted evil withcraft.)
I've read a report about "witch salve" somewhere on the web - some medical students brewing up a salve of pig fat (lard), thorn apple / jimson weed, nightshade/banewort, and other supposed ingredients of witch salve. A female volunteer then "rode the broomstick" (= applied the salve to the mucous membranes in her genital area), and promptly had all the symptoms reported for the witches' carnival / bedevilment / esbat:
Loss of orientation, a feeling of flying and being yanked through the air, horror hallucinations, sexual arousal, and a bit later vomiting and stomach cramps. They descriibed it, iirc, as being a bit like a very bad LSD trip except you're constantly falling from a great height and have the strong urge to get yourself penetrated by bladed tentacles.
... as for DF, hmm, I'm not sure addictive drugs would make that much fun as an addition. They weren't any fun in Fallout either, imo.
Implementing it would be easy though: Dwarves with a personality trait e.g. "fond of the herb" could e.g. grab some plant - rope reed or pig tail, depending on whether they prefer Indoor or Outdoor - and smoke it during their break. :-)