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

BackgroundPsychedelic 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.MethodsWe 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).ResultsThree 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-HT2B activation remain uncharacterized.ConclusionsCurrent 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.