One early study of psychedelics used niacin as the placebo. All the patients were in the same room (not a great study design IMO) All of the control patients ex

One early study of psychedelics used niacin as the placebo. All the patients were in the same room (not a great study design IMO) All of the control patients experienced niacin flushing before the treatment patients started having effects, so many treatment patients initially thought they were in the control group.