I think it'd be cool if certain types of drugs, and I haven't tried any yet so I don' know if this has been introduced already I'm just guessing it hasn't, would affect the environment surrounding the player itself.
For example, some drugs could make other characters, NPC or note, positioned in the same room as the player type out certain phrases or poses that didn't correspond to reality, that yet were driven by the drug effect in order to provide an interesting experience to the player using them although contributing to a certain sense of confusion and mix between reality and illusion.
Also, certain types of drugs could eventually teleport players to paralel worlds designed to make the player belief he's actually there although his player would remain inside the room where the drug had taken effect, although certain messages would be seen by other players to remind them that the one taking the drugs is actually tripping and not psychologically there.
Certain experiences could also have long term effects that would affect the way the player interacts with others surrounding him, mix-matching certain phrases of his, or typing out involuntary poses that would reflect his addiction.
Once again I want to make clear that I don't know if any of this was already introduced, just think it would be cool if it hasn't.
'd like to know what you think 'bout this, thnx.