[Kereth]

I know RetroMUD has some drugs, with effects such as hallucinations, and even used to have a guild with drug usage as a minor part of its theme (the Hand Guild, as an assassin guild vaguely resembling Marco Polo's version of the hashasheen, though it's been revamped into the Assassin Guild, a more tactically interesting shift, which cut out the drugs and religious skills. There are still drugs and hallucinations and such around though.)

I believe DiscworldMUD also has some drugs, though I'm fuzzy on the details. They've got a number of snacks and drinks which make your character act oddly, and I at least suspect their might be some actual drugs in the mix somewhere, but I can't think of where they'd be at exactly.