The use of low sub-perceptual doses of psychedelics ("microdosing") has gained popularity in recent years. Although anecdotal reports claim multiple benefits associated with this practice, the lack of placebo-controlled studies severely limits our knowledge of microdosing and its effects. Moreover, research conducted in standard laboratory settings could fail to capture the motivation of individuals engaged or planning to engage in microdosing protocols, thus underestimating the likelihood of positive effects on creativity and cognitive function. We recruited 34 individuals starting to microdose with psilocybin mushrooms (Psilocybe cubensis), one of the materials most frequently used for this purpose. Following a double-blind placebo-controlled experimental design, we investigated the acute and short-term effects of 0.5 g of dried mushrooms on subjective experience, behavior, creativity (divergent and convergent thinking), perception, cognition, and brain activity. The reported acute effects were significantly more intense for the active dose compared to the placebo, but only for participants who correctly identified their experimental condition. These changes were accompanied by reduced EEG power in the theta band, together with preserved levels of Lempel-Ziv broadband signal complexity. For all other measurements there was no effect of microdosing except for few small changes towards cognitive impairment. According to our findings, low doses of psilocybin mushrooms can result in noticeable subjective effects and altered EEG rhythms, but without evidence to support enhanced well-being, creativity and cognitive function. We conclude that expectation underlies at least some of the anecdotal benefits attributed to microdosing with psilocybin mushrooms.

Departamento de Física Universidad de Buenos Aires and Instituto de Física de Buenos Aires CABA Buenos Aires Argentina

Department of Cognitive Science and Artificial Intelligence Tilburg University Tilburg the Netherlands

Department of Experimental Neurobiology National Institute of Mental Health Klecany Czech Republic

Forensic Laboratory of Biologically Active Substances Department of Chemistry of Natural Compounds University of Chemistry and Technology Prague Prague Czech Republic

Fundación para la Lucha contra las Enfermedades Neurológicas de la Infancia Montañeses 2325 C1428 CABA Buenos Aires Argentina

Institute of Cognitive and Translational Neuroscience INECO Foundation Favaloro University Buenos Aires Argentina

Latin American Brain Health Institute Universidad Adolfo Ibañez Santiago de Chile Chile

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