Is it possible to have a placebo group when doing a study on psilocybin? Would participants in the placebo not notice the lack of psychedelic effects?

EDIT: In the original link it says the placebo group received a much lower dose, so that seems to be one way of doing it.

There was a placebo group that were given basically a very strong antihistamine which induced some drowsiness.

This particular trial, however, allowed participants who were in the placebo group to later opt in for the real dosing - obviously with those results omitted from the trial.