What would be the scientific usefulness of a control group? It's my understanding that the effect could not reasonably be confused with placebo. There are plenty of other studies on treatment of depression; although, there is always the slight risk of a general societal upwelling of good feelings or its complement.
Psilocybin treatment is given in a therapist's office in conjunction with therapy so, yes, there could well be very positive effects for patients having that therapy experience with a placebo.
