eh... I think Tarn might want to keep drugs out of the game.
But... Judging by the fact that we're always rewarded with extremely gruesome descriptions of bodily dismemberment when combat occurs, and there's an extremely large quantity of alcohols to obtain.. Something tells me that wouldn't be out of place.
I don't think it should cause murders, though, maybe some other nasty side effects, like... well, indecency, maybe a small brawl and waking up next to someone unattractive and unfamiliar. Murders would be rare. If you're smart in nethack, you can generally avoid corpsifying anyone you don't want to be a corpse while hallucinating. Examples being using #chat or my method: trip out in the closet instead.
I think it should also fall under ethics. Some dwarven cultures will look down upon altering ones consciousness with ingested fly agaric mushrooms, while most elves might be a bit more... hippy ish, man!
Perhaps hallucination should also be a syndrome effect. Them forgotten beasts be blasting muscimol out of their faces.
I'm having a lot ideas that should probably go in a new topic...
at this point, I think that's the point of this thread, with it branching out into the chitin thread. It's become one of the many "particularily large pile of mostly previously discussed suggestions." (Except I searched chitin a bit, I didn't find alot of anything.)