DATE: July 21, 2025 at 06:00AM
SOURCE: PSYPOST.ORG

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TITLE: Cognitive tests suggest psilocybin impairs thinking—but the tests may not tell the full story

URL: psypost.org/cognitive-tests-su…

New research published in the journal Psychopharmacology shows that psilocybin—the psychedelic compound found in certain “magic” mushrooms—slows reaction time and impairs executive functioning during its acute effects. The study, a systematic review and meta-analysis of 13 experiments, found that people under the influence of psilocybin responded more slowly to cognitive tasks and, to a lesser extent, made more errors, particularly at higher doses.

Psilocybin has gained renewed attention in recent years due to its potential therapeutic effects for depression, anxiety, and substance use disorders. While many studies have explored how the drug affects emotions and mood, far less is known about how it influences cognitive functioning—particularly executive functions such as working memory, attention, and self-control.

These abilities are vital to daily functioning and may also be relevant to therapeutic outcomes. For example, executive function deficits are common across many forms of mental illness. Understanding whether psilocybin worsens or improves these abilities is important for assessing both the safety and the therapeutic potential of the compound.

“Cognitive functions are a crucial but underexplored aspect of psychedelic science,” said study co-authors Morten Lietz and Parsa Yousefi, who are both PhD candidates affiliated with the Molecular Psychiatry Lab at the University of Fribourg.

“Researching anything that involves structured tasks—like those requiring participants to sit and concentrate during a psychedelic experience—is inherently challenging. Since some of our future projects aim to assess cognitive functions in psychedelic trials, we wanted to get a comprehensive overview of the existing literature to understand where we can contribute meaningfully to the field.”

The researchers conducted a comprehensive review of existing studies that measured how psilocybin affects executive functions and attention during its acute effects—usually within four hours of administration. They searched several major research databases and selected peer-reviewed studies that tested participants under the influence of psilocybin using standardized cognitive tasks.

In total, the researchers identified 13 studies that met their criteria, which together provided 42 separate comparisons between people who took psilocybin and those who received a placebo. The tasks measured five domains: working memory (such as updating information in mind), conflict monitoring (resolving interference between competing inputs), response inhibition (resisting impulsive actions), cognitive flexibility (shifting strategies), and attention.

The researchers used multilevel meta-analysis techniques to account for differences between studies and to examine moderators like dose, timing, and the type of task. A meta-analysis is a statistical method that combines data from multiple studies to identify overall patterns and effects. They focused on two core performance metrics: reaction time (how fast participants responded) and accuracy (how often they responded correctly).

Across all studies, psilocybin was associated with a large and statistically significant slowing of reaction time during its acute effects. The overall effect size was Hedges’ g = 1.13, meaning participants took noticeably longer to respond to cognitive tasks when on psilocybin compared to placebo.

The impact of psilocybin on accuracy was less clear. On average, accuracy was slightly lower under psilocybin (Hedges’ g = -0.45), but this result was not statistically significant. This suggests that while people under psilocybin take longer to respond, they do not necessarily make many more mistakes—though accuracy was reduced in some individual studies.

Importantly, the researchers found that the type of task influenced the size of the effect. Psilocybin’s impact on reaction time was more pronounced when tasks measured general performance rather than isolating a specific cognitive skill. For instance, tasks that required general attention and motor speed showed stronger effects than those that carefully controlled for these factors. This suggests that much of the impairment may stem from broad effects on attention, motivation, or motor control, rather than specific disruptions to higher-order executive functions.

The researchers noted that traditional lab tasks may not be well suited to measuring cognitive performance during a psychedelic experience. Many of these tests are repetitive and abstract, which may make them feel irrelevant or unengaging to people undergoing a deeply altered state of consciousness.

“In this project, we reviewed all available scientific papers that assessed cognitive functions during the acute effects of psilocybin,” Lietz and Yousefi told PsyPost. “We found that psilocybin tends to impair certain higher-order cognitive functions during that timeframe, largely independent of the dosage. Initially, this raised concerns—but our deeper analysis revealed something interesting: the less precise the cognitive tests were, the stronger the reported impairments.”

“This led us to question whether conventional cognitive tests—designed for sober individuals—are suitable for assessing cognition during altered states of consciousness. For example, participants under the influence of psilocybin may be less inclined to engage with repetitive computer tasks while undergoing what Griffiths et al. (2006) described as one of the most meaningful experiences of their lives.”

“Others may simply find it difficult to focus on identifying the color of a letter while immersed in intense, psilocybin-induced visual distortions,” the researchers explained. “Taken together, our results suggest that in order to understand how psilocybin truly affects cognition, we need new testing approaches—ones that work with the psychedelic experience, rather than against it.”

As with all research, the study has limitations. First, it only examined the short-term effects of psilocybin during the acute phase. There is some evidence that psilocybin may actually improve cognitive functioning in the days or weeks after use, but these long-term effects were not captured in this analysis.

Second, the included studies varied widely in their methods, participant samples, and cognitive tasks, contributing to statistical heterogeneity. Some studies had small sample sizes, and there was evidence of publication bias—meaning that studies showing no effects may have been less likely to be published.

“As a meta-analysis, we relied on data from original studies,” Lietz and Yousefi noted. “If those studies contained biases, our results would be influenced as well. Indeed, our risk-of-bias analysis revealed that some studies had potential limitations—most notably regarding blinding, which is a known challenge in psychedelic research.”

To address these limitations, the authors suggest that future research should explore psilocybin’s effects across longer time frames and use more naturalistic or engaging tasks. They also recommend incorporating tools like eye tracking or experience sampling to gain insight into real-world cognitive changes during and after the psychedelic experience.

“Our next goal is to explore how psychedelics might affect cognition in the long term—and whether they could potentially enhance learning, memory, executive functions, or creativity,” Lietz and Yousefi said.

The research team is pursuing several projects focused on psychedelics and cognition. One study is investigating creative thinking in healthy individuals, while another is exploring the combined use of neurofeedback and psilocybin to enhance cognitive performance. An ongoing study is also examining how LSD affects neuroplasticity and age-related cognitive function in older adults.

“We’re currently recruiting! We’re looking for healthy, German-speaking individuals over the age of 60 living in Switzerland for the LSD study,” the researchers added. “More information is available on our website.”

The study, “Acute effects of psilocybin on attention and executive functioning in healthy volunteers: a systematic review and multilevel meta-analysis,” was authored by P. Yousefi, Morten P. Lietz, F. J. O’Higgins, R. C. A. Rippe, G. Hasler, M. van Elk, and S. Enriquez-Geppert.

URL: psypost.org/cognitive-tests-su…

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