The subtle science: a systematic review of psilocybin magic mushroom and truffle microdosing.

Introduction: Microdosing psilocybin magic mushrooms (MM) and truffles has grown in popularity, but the evidence supporting reported benefits remains poorly characterized. The purpose of this systematic review was to synthesize the existing literature on microdosing psilocybin MM and truffles in adults to determine reported health effects and perceived benefits, motivations for use, dosing protocols and preparations, adverse events, and competing interests. Methods: This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and was registered with the International Prospective Register of Systematic Reviews (PROSPERO; CRD42023428107). Studies of adults microdosing psilocybin MM or truffles were eligible. Risk of bias was assessed across included studies. Results: Eleven articles (five quantitative and six qualitative studies) met inclusion criteria. Studies were conducted in the United States (n=4), Netherlands, Argentina, and internationally (n=2 each), and Slovenia (n=1) with a total sample of 3,262 adults. Some studies reported microdosing psilocybin MM or truffles may improve well-being, mental health, cognition, physical health, creativity, relationships, pain, curiosity, and substance dependence, and enhance senses among adults. However, the majority of evidence had at least some concerns for risk of bias or was qualitative and used a variety of self-reported outcome measures. Approximately 86% of microdoser motivations were non-medical and only 14% were related to medical diagnoses, mostly for mental health improvements. Extreme heterogeneity was identified across dosing protocols and preparations. The majority of studies did not report adverse events but for those reported, they were mostly mild. All but four studies declared no conflicts of interest and four did not disclose funding sources. Discussion: The certainty of the evidence is low, and a causal effect of microdosing cannot be inferred. Future research should prioritize well-powered randomized controlled trials with standardized and substance-specific dosing protocols to determine causal relationships between microdosing MM or truffles and health outcomes. Mandatory reporting of adverse events and funding sources should be implemented to build the safety profile of microdosing MM and truffles and ensure transparency for potential conflicts of interest. Sytematic review registration: https://www.crd.york.ac.uk/prospero/, identifier CRD42023428107.