Abstract
Dear Editor,
The recent article by Kerr-Gaffney et al. (2026) looked at how psilocybin affects personality, mental health symptoms, and personal values in healthy volunteers (Kerr-Gaffney et al., 2026). While the study tries to explain how psychedelics can lead to psychological change, some parts of the study design and interpretation deserve further discussion.
The authors mention that participants may have been able to tell whether they received psilocybin or placebo. However, this issue may have a larger effect on the results than the authors suggest. Psilocybin produces strong and recognizable effects, so participants likely knew which group they were in. When this happens, people’s expectations about personal growth or transformation, especially ideas they may have heard about psychedelics, can influence how they report their experiences. This makes it harder to know whether the reported changes were caused by the drug itself or by expectations. In addition to this, participants in psychedelic studies often self-select to participate, and may already hold positive attitudes toward psychedelics or expectations of personal insight and growth. This kind of selection bias may further increase the likelihood of reporting positive psychological or value-related changes, independent of the pharmacological effects of psilocybin.
Importantly, the differences between the psilocybin and placebo groups appeared only on the Life Changes Inventory (LCI), which asks participants to report changes they believe happened since the experience. No significant differences were found on established measures of personality (NEO-FFI), psychiatric symptoms (SCL-90), or cognitive flexibility (IED). Because the effects appeared only on a subjective self-report measure and not on widely used psychological scales, it is unclear if the results show real psychological change or simply how participants interpreted their experience afterward.
Another concern is that the LCI was originally designed to study near-death experiences and has rarely been used or validated in psychedelic research. Other related measures in the study, such as empathy and social responsibility, did not show significant changes even though they overlap with several LCI categories. This difference suggests that the reported value changes should be interpreted with caution.
The authors also suggest that the feeling of “oceanic boundlessness” explains the reported changes. While this idea is interesting, the analysis is based on correlations and self-report measures for both the cause and the outcome. Because the study did not measure participants’ values before the experience, and because participants likely knew which treatment they received, it is difficult to draw strong conclusions about cause and effect. Additionally, the follow-up period in the study was relatively short (12 weeks). Personality traits and personal values are typically considered stable, long-lasting constructs that change slowly over time. Observing changes over such a short interval makes it difficult to determine if the reported effects reflect lasting psychological change or more temporary shifts in perception and interpretation following the experience.
Finally, the participants in the study were mostly healthy, white, highly educated individuals, and many had previously used psilocybin. Although this is common in early research, it limits how widely the findings can be applied. People with severe or treatment-resistant mental health conditions come from much more diverse backgrounds. Results from relatively privileged and educated samples may not fully apply to the broader populations who may eventually seek psychedelic-assisted treatments. Future studies should include more diverse participants to improve both scientific accuracy and fairness.
Future research using active comparison treatments, measuring personal values before and after treatment, and using well-validated measures of psychological change will be important for separating true drug effects from changes caused by expectations.
