Expectancy in placebo-controlled trials of psychedelics: if so, so what?

Expectancy and unblinding in psychedelic trials likely cause overestimation of treatment effects, but this problem is not unique to psychedelics. The authors argue that premature hype directly inflates participant expectations, yet placebo-controlled RCTs are imperfect for many therapies and blinding issues should not automatically disqualify medications from approval. Practical measures like independent raters and active placebos can partially mitigate these effects, and alternative methods such as naturalistic studies can supplement RCT results. Early data should neither be dismissed nor taken as firm evidence of effectiveness.

Study at a glance

Abstract

Modern psychedelic research remains in an early phase, and the eventual introduction of psychedelics into clinical practice remains in doubt. In this piece, we discuss the role of blinding and expectancy in psychedelic trials, and place this in a broader historical and contemporary context of blinding in trials across the rest of healthcare. We suggest that premature and uncritical promotion ('hype') of psychedelics as medicines is not only misleading, but also directly influences participant expectancy in ongoing psychedelic trials. We argue that although psychedelic trials are likely to significantly overestimate treatment effects by design due to unblinding and expectancy effects, this is not a unique situation. Placebo-controlled RCTs are not a perfect fit for all therapeutics, and problems in blinding should not automatically disqualify medications from licencing decisions. We suggest that simple practical measures may be (and indeed already are) taken in psychedelic trials to partially mitigate the effects of expectancy and unblinding, such as independent raters and active placebos. We briefly suggest other alternative trial methodologies which could be used to bolster RCT results, such as naturalistic studies. We conclude that the results of contemporary placebo-controlled RCTs of psychedelics should neither be dismissed due to imperfections in design, nor should early data be taken as firm evidence of effectiveness.