Classical psychedelic microdosing, mood, and cognitive function: An umbrella review with narrative synthesis

Background: Psychedelic microdosing—repeated sub-perceptual doses of lysergic acid diethylamide (LSD) or psilocybin—has attracted scientific interest as a potential mood and cognitive intervention. The evidence base remains methodologically heterogeneous and vulnerable to expectancy bias. Methods: We conducted an umbrella review with narrative synthesis following Joanna Briggs Institute guidance and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 standards (International Prospective Register of Systematic Reviews [PROSPERO]: 2020 standards (PROSPERO: CRD420251077340). Six databases were searched through February 2026. Eligible studies were systematic reviews and/or meta-analyses examining microdosing effects (⩽20 μg LSD or ⩽3 mg psilocybin per session) on mood or cognitive outcomes in adults. Quality was appraised with A Measurement Tool to Assess Systematic Reviews-2; primary-study overlap was quantified via corrected covered area (CCA). Results: Three meta-analyses met quantitative criteria, drawing on 14 studies (13 unique samples, N = 1614); three reviews contributed to narrative synthesis. Primary-study overlap was very high (CCA = 0.29). The sole significant pooled effect was a small decrease in cognitive control ( d = −0.34, 95% CI: −0.62 to −0.06); all other domains were non-significant. No eligible meta-analysis provided pooled mood-outcome effect sizes within the microdose threshold; narrative evidence indicates that self-reported mood benefits are largely attenuated under placebo-controlled conditions. Short-term tolerability was acceptable, though cardiovascular signals and long-term risks via 5-HT 2 B activation remain uncharacterized. Conclusions: Current evidence does not support cognitive enhancement through microdosing; the only consistent controlled finding runs counter to popular claims: microdosing was associated with a small but reliable impairment of cognitive control. Observed mood benefits are not replicated under blinded conditions, consistent with expectancy-driven responding. Adequately powered, preregistered, expectancy-controlled trials are required before clinical recommendations can be made.