Psychotropic pharmaceuticals can have strong interactions with legal and illegal drugs alike. If you're taking most types of these, you won't want to smoke pot or drink alcohol. Also, since you can't depend on the ingredients and dosages of illegal or unregulated drugs, there is really no telling what drugs you could or couldn't take in concert with your psychotropics.

And then there are questions of whether you'll tell your psychiatrist. I've seen a quite accepting, non-judgemental attitude about recreational drugs, but can you count on this to be consistent? Do you want this on record in your medical chart? Do you want to try and consistently lie about activities quite germane to your mental health?