https://doi.org/10.1177/0269881120908004 Journal of Psychopharmacology 1–11 © The Author(s) 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0269881120908004 journals.sagepub.com/home/jop Introduction Microdosing refers to the use of a low, typically sub-perceptual dose of a pharmacological substance. In the context of the use of classic psychedelic drugs – for example lysergic acid diethyla- mide (LSD) and psilocybin (psilocin) – microdosing refers to ingesting sub-hallucinogenic amounts of the substance, approxi- mately 1/10th of what would be considered a standard psychoac- tive dose (Fadiman, 2011; Kuypers et al., 2019). The classic psychedelics are a group of compounds that share 5-HT2A receptor agonist properties, and which, at higher doses, induce profound alterations in thought, perception, and emotion (Halberstadt, 2015; Nichols, 2016; Rickli et al., 2016), along with experiences of ego dissolution (Letheby and Gerrans, 2017; Milliere, 2017), and/or mystical-type experiences (Griffiths et al., 2011; Liechti et al., 2017). Various studies have demon- strated the safety and low addiction potential of psychedelics in healthy and clinical populations (Johnson et al., 2018; Nichols, 2016). In addition, recent studies have reported the potential effi- cacy of psychedelic-assisted psychotherapy for patients with anxiety associated with advanced cancer and other life-threaten- ing illnesses (Gasser et al., 2014; Griffiths et al., 2016; Grob et al., 2011; Ross et al., 2016), alcohol use disorder (Bogenschutz et al., 2015), tobacco use disorder (Johnson et al., 2014), and major depressive disorder (Carhart-Harris et al., 2016). Coverage of microdosing in popular media in recent years – including features in Rolling Stone (2015), Wired (2016), and The New York Times (2017) – has described some purported benefits of microdosing psychedelics, such as alleviating depression, migraines, and chronic-fatigue syndrome; improving concentra- tion and reducing anxiety; and enhancing creativity (Leonard, 2015; Solon, 2016; Waldman, 2017a). In addition, anecdotal reports suggest that microdosing may improve cognitive perfor- mance (Waldman, 2017b; Wong, 2017). Despite these reports, there remains a dearth of academic research describing the prac- tice of microdosing, including the specific substances consumed, doses and dosing schedules, and relevant demographic data of microdosers. Few scientific articles on microdosing among human subjects have been published, including two by our group Microdosing psychedelics: Demographics, practices, and psychiatric comorbidities Daniel Rosenbaum 1 , Cory Weissman 1 , Thomas Anderson 2 , Rotem Petranker 3 , Le-Anh Dinh-Williams 4 , Katrina Hui 1 and Emma Hapke 1 Abstract Rationale: Microdosing psychedelics – the practice of consuming small, sub-hallucinogenic doses of substances such as LSD or psilocybin – is gaining attention in popular media but remains poorly characterized. Contemporary studies of psychedelic microdosing have yet to report the basic psychiatric descriptors of psychedelic microdosers. Objectives: To examine the practices and demographics of a population of psychedelic microdosers – including their psychiatric diagnoses, prescription medications, and recreational substance use patterns – to develop a foundation on which to conduct future clinical research. Methods: Participants (n = 909; M age = 26.9, SD = 8.6; male = 83.2%; White/European = 79.1%) recruited primarily from the online forum Reddit completed an anonymous online survey. Respondents who reported using LSD, psilocybin, or both for microdosing were grouped and compared with non-microdosing respondents using exploratory odds ratio testing on demographic variables, rates of psychiatric diagnoses, and past-year recreational substance use. Results: Of microdosers, most reported using LSD (59.3%; M dose = 13 mcg, or 11.3% of one tab) or psilocybin (25.9%; M dose = 0.3 g of dried psilocybin mushrooms) on a one-day-on, two-days-off schedule. Compared with non-microdosers, microdosers were significantly less likely to report a history of substance use disorders (SUDs; OR = 0.17 (95% CI: 0.05–0.56)) or anxiety disorders (OR = 0.61 (95% CI: 0.41–0.91)). Microdosers were also more likely to report recent recreational substance use compared with non-microdosers (OR = 5.2 (95% CI: 2.7–10.8)). Conclusions: Well-designed randomized controlled trials are needed to evaluate the safety and tolerability of this practice in clinical populations and to test claims about potential benefits. Keywords Psychedelics, microdosing, psilocybin, LSD, substance use 1 Psychiatry, University of Toronto Faculty of Medicine, Toronto, Canada 2 Psychology, University of Toronto, Toronto, Canada 3 Psychology, York University, Toronto, Canada 4 Clinical Science, University of Toronto, Scarborough, Canada Corresponding author: Daniel Rosenbaum, Psychiatry, University of Toronto Faculty of Medicine, 250 College Street, 8th Floor, Toronto, ON M5T 1R8, Canada. Email: daniel.rosenbaum@mail.utoronto.ca 908004JOP 0 0 10.1177/0269881120908004Journal of PsychopharmacologyRosenbaum et al. research-article 2020 Original Paper