It might be neat if drugs were folded in with poisons, and have the FO:NV poison mechanics [used for melee weapons], be extended to other objects.
I remember playing a game where the player faced a guardian that they could never defeat; a gargoyle, but he was slow to rise, so you could usually run from him, but the player could light a poisoned candle and leave it in the room... after a while the gargoyle drops dead. I think that could even be done with a scripts in Oblivion. One for the poisoning of the wax, and the other for the area effect cloud of the gas.
I suppose a drugged candle would affect everyone in the room. I don't think a healing drug would make sense in this case (healing everyone in the room), but drugs that add a small bonus or penalty might work well. *Not just on candles of course... mugs, cups, and food items; traps. Imagine being able to drug a guard, and have them display the drug effects as a diversion, while the PC sneaks past several others that respond to the drugged guard's disturbance.
Come to think of it... The Witcher handled drugs pretty well (I thought).