[tpm]

The measures that were taken to keep people "safe" were definitely a factor. In psychedelic circles it's called 'set and setting' and it is an integral part of the experience. Under the influence of psychedelics, one is much more susceptible to the information from the environment.

I don't think it's possible to do fully blinded studies with psychedelics. However in an older study (Griffiths I think) they gave placebo or psilocybin to the participants on random basis, but eventually everyone had one experience with placebo and one with psilocybin. The measured effects did clearly distinguish between placebo and psilocybin.