Comment by jrowley

The tricky thing about psychedelics is that they have been described as delivering the "placebo effect on steroids". That is to say, the set and setting prior to ingestion directly effects outcomes, so if you want to maximize your chance of seeing some consistent results, you would want to prime people with certain expectations and knowledge prior to them taking the psychedelic. If you were to control it against an active placebo (people often use an amphetamine), the participants would be able to deduce they aren't actually taking a psychedelic.