Not counting alcohol which is ubiquitous, there are some hints to drug usage here and there. Rogues can pick pocket some snuff and other tobacco / smoking paraphernalia. There’s also a handful of herbs that (iirc) have mention of being addictive (Bloodthistle) and some that have rather interesting interactions when harvested (Nightmare Bloom, Dreaming Glory just off the top of my head).
Only other instances I can think of is mana its self being portrayed as physically addictive in Burning Crusade. Sadly that was never outright stated what it’s overall attributes are when you become addicted to consuming mana, just hinted at.
All that said, the only non-TOS-violating way I can think of to use drugs would either be getting soused or by packing your pickpocketed [Hickory Pipe] and having a puff of…idk, Peacebloom? Just tread carefully.