Klaark
When I write stories, I don't envision them being used as guides to life, so I don't mind writing about people abusing drugs and making poor decisions.
What bugs me about fantasy settings is this need to come up with fake drugs. Ale, mead, all fine, but we need to substitute some bullshit if we want cocaine or another opiate thrown in there. Guess crack isn't medieval-sounding enough...
You hear about how they supposedly found cocaine on some mummies? Pretty hilarious stuff. One guy still had part of a beetle carcass in him (I think it was the first attempt at a red M&M).
Kaiser, I fail to see how those are different from 'magic' potions. Magic potions in fantasy have always caused super-powers, and yet I've never seen it treated in a context where they were drugs/'bad'. Not in the realistic sense that many drugs are, anyways.
It depends on whether or not you see them as drugs, though. Your own personal bias will probably reflect a lot in your writing. Remember, too, that there are many beneficial drugs/'magic' in life; pain-killers, vitamin and mineral tablets, vaccines, so forth. You might want to figure out where you personally draw the line of 'bad drugs' as well, so as to avoid it or cross it at will.
Personally, I agree with Klaark. I'm a little tired of fantasy settings that try to apply good or 'Disney dressings' to a time that was horrific and disgusting. I would love to read about some warrior going between snorting crack off of some no-toothed eighty-year old brothel worker's knee and trying to fight a dragon while wondering about his next fix. Everyone does the grouchy old alcoholic who miraculously pulls through for everyone in the last bit; I'd love to see that subverted, too.
But, that's a story not many people are interested in writign, much less reading, haha. Again, it all comes back to what you want out of it; don't worry how it will look to others.
(I say this while avoiding a social taboo in my own story so I won't be accused of committing it in real life. Woo, go hypocrites! )