If all participants have never tried psychedelics, maybe it could be tested against a non-psychedelic psychoactive drug so both groups would feel something?
Doesn't help: any normal person can tell the difference between a full dose of psilocybin and a low dose of amphetamines.
"You'll be given either a psychedelic or a stimulent, followed by x testing" - then knowing which drug you're getting doesn't mean you know if you're in the placebo group or not?