Expectancy bias in psychedelic trials can inflate reported benefits by shaping participant experiences, blinding failure, and the interpretation of outcomes in psilocybin research

Expectancy bias in psychedelic trials can make treatments look more effective than they are by altering what participants feel, report, and expect to gain. Psychedelic studies are especially vulnerable because the acute effects are obvious, blinding often fails, and cultural hype around compounds like psilocybin can prime both volunteers and researchers. Psilocybin research sits at the center of this problem because participants may correctly guess whether they received an active dose, then rate symptom changes through that lens. Trial design choices such as weak placebos, therapist enthusiasm, and media-driven expectations can further amplify perceived benefit. Better controls, stronger blinding strategies, and more rigorous study design matter because clinical enthusiasm, investor interest, and public policy may otherwise move faster than the evidence. Separating drug effects from expectancy effects is central to judging real therapeutic value.