How do you do a double-blind with a drug that perceptibly changes your state of mind?

I guess you do it anyway? the change in the state of mind is thought to be at least in part the mechanism of action, no? so if thats what makes it work, its good to test it against a non hallucinogen

You can't, and it's a real problem for some people. Other people realize that, like testing the efficacy of parachutes by throwing two people off an airplane, one without a parachute; other people realize the double blind standard can't be applied but that the results aren't woo mystical astrology unfounded conclusions despite that.