Classic psychedelics and personality: An updated systematic review.

Abstract

<h4>Background</h4>The impact of classic psychedelics (5-HT2A receptor agonists) on personality traits has been studied for decades, and it has been hypothesized that the mechanisms underlying these changes are linked to agonism at cortical serotonergic 5-HT_2A receptors. However, research results are contradictory. Therefore, the present paper aims to systematically evaluate the effects of psychedelics on personality, updating (2016-2024) a previous systematic review by Bouso and collaborators (2018). The International Prospective Register of Systematic Reviews ID for this study is CRD42024582704.<h4>Method</h4>Systematic review using four databases (PubMed, LILACS, PsycINFO, and SciELO) including randomized controlled trials, open-label, and observational studies. Interventions included the consumption of any classic psychedelic (lysergic acid diethylamide, psilocybin, ayahuasca/dimethyltryptamine, mescaline), and the studies were required to use some instrument for personality assessment. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to conduct the data collection.<h4>Results</h4>Out of 6043 references screened, 48 studies were included: 14 experimental and 34 observational. The most consistent findings were increases in <i>Openness</i> and reductions in <i>Neuroticism</i>, especially with psilocybin and ayahuasca. Changes in other traits, such as <i>Extraversion</i>, <i>Agreeableness</i>, and <i>Conscientiousness</i>, were more variable. Microdosing was associated with modest reductions in <i>Neuroticism</i> and higher <i>Absorption</i>. Most studies used instruments based on the Five-Factor Model, reflecting its growing dominance.<h4>Conclusions</h4>Classic psychedelics seem to promote lasting personality changes, most consistently increasing <i>Openness</i> and reducing <i>Neuroticism</i>. Future research would benefit from combining experimental and naturalistic designs, using longer follow-up periods and more diverse personality models to better understand the interplay between psychedelics and personality, thus providing a more accurate guide for clinical use.

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