Expectancy Effects in Naturalistic Psilocybin Use in a Dutch Smartshop

Abstract

In recent years, psychedelic research has focused largely on its clinical use in laboratory settings (Carvalho et al., 2025; Pallavicini et al., 2021; van Elk & Yaden, 2022). However, most people use naturalistic psychedelics recreationally, and the number of individuals doing so is rising, as reported by the Global Drug Survey (Winstock et al., 2022; Nayak et al., 2023). This study aims to provide deeper insight into the effects of naturalistic psilocybin use, in particularly how personality traits and expectation predict more pleasant or challenging psychedelic experiences. This knowledge can contribute to harm reduction in recreational use of psilocybin and in providing insight on the safety of using naturalistic products. This study is part of the larger project “Assessing the effects of psilocybin truffles in a Dutch Smartshop” (Cardeña, 2025). This sub-component of the project will investigate whether expectations for the psychedelic experience predict the subjective psychedelic experience. Expectations will be measured by the single-item version of the 11-Dimensional Altered States of Consciousness Scale administered before truffle ingestion (Brief ASC; Marschall et al., 2023). The ongoing subjective effects will repeatedly be tracked with a valence grid and a visual analogue scale. Additionally, subjective effects will be measured post psychedelic experience by administering the brief ASC again.

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