I don't have a citation on hand, but I know one of the early psilocybin experiments (of seminary students, so probably prone to spiritual response) used niacin

I don't have a citation on hand, but I know one of the early psilocybin experiments (of seminary students, so probably prone to spiritual response) used niacin as the control compound. These were drug-naive test subjects so having no response at all would have unblinded the experiment. Niacin, in enough of a dose, causes tingling, flushing, and heart rate changes.