Effects of psychedelic microdosing on cognitive functions: A systematic review and meta-analysis.

Microdosing - the practice of consuming extremely low doses of classical psychedelic substances that do not elicit overt psychedelic effects - has gained significant attention as a potential method for enhancing cognitive performance. However, findings from controlled studies remain mixed and inconclusive. This preregistered meta-analysis examined the cognitive effects of classical psychedelic microdosing in 14 different studies (N = 1614), analyzing 59 effect sizes across multiple cognitive domains, spanning both acute (on-drug) and post-acute (off-drug) assessments. Results show a significant decrease in cognitive control, with no detectable effects on other cognitive domains or in general. Neither substance type (psilocybin or LSD), dosage (0.1-0.5 g psilocybin; 6.5-20 g LSD), nor microdosing duration (1-42 days) emerged as significant moderators. Assessment timing (on- vs. off-drug) likewise did not moderate the effects. These findings suggest that microdosing may disrupt top-down cognitive control processes, aligning with cognitive and neural models of how classical psychedelics alter information processing in the brain to reduce rigidity and enable more fluid states of consciousness. However, better distinguishing between on-drug and off-drug effects is essential for clarifying whether microdosing exerts only transient pharmacological influences or promotes lasting cognitive change. Given the methodological heterogeneity across studies, future research using standardized protocols and mechanistic approaches is needed to fully characterize the cognitive and neural effects of microdosing classical psychedelics.