Selection bias may inflate reported psychedelic benefits, as a new study finds more positive outcomes among users who stay engaged in survey research

Selection bias may overstate the benefits of psychedelics when people with positive experiences are more likely to remain in survey studies and report outcomes over time. The central concern is that observational psychedelic research can systematically miss participants with neutral, negative, or less dramatic effects, making results look more favorable than they really are. The study highlights attrition as a key mechanism behind this distortion. People who feel helped may be more motivated to keep responding, while those who experience disappointment, adverse effects, or no meaningful change may drop out. That pattern can skew estimates of improvements in mental health and wellbeing. The finding matters because much of the public enthusiasm around psychedelics relies on self-selected samples and naturalistic designs rather than randomized controlled trials. Stronger recruitment, retention, and follow-up methods are needed to separate genuine therapeutic effects from biases in who chooses to participate and who stays in the data.