Background: Insight - a sudden change in understanding or perspective that feels true or reliable - is a common occurrence during psychedelic experiences, and often considered by clinicians and patients to be central to their therapeutic value. However, their occurrence and role has not been systematically assessed.
Objectives: We reviewed all peer-reviewed studies that published data on insight catalysed by a classic psychedelic at psychoactive levels to elucidate several aspects of psychedelic-catalysed insight, including its prevalence, relationship to dose, time-course, and relationship to therapeutic outcomes. Risk of bias was assessed regarding selection, reliability, causality, and transparency. PROSPERO registration: CRD42023405854 FINDINGS: The final database and key bibliography searches were completed on July 13, 2024. We screened 741 abstracts and included 98 studies (40 survey, 58 interventional). Insight was positively correlated with psychedelic dose, and was significantly higher following psychedelics in 43 of 46 (93 %) studies that presented a comparison to a placebo condition. Crucially, 25 of 29 studies (86 %) found that insight was associated with therapeutic improvement, and this relationship was often stronger than mystical-type experience, which has received more research attention.
Interpretation: This review indicates that psychedelic-catalysed insight is associated with therapeutic improvement, suggesting its importance for clinical practice and for understanding the mechanisms of psychedelic therapy.
Limitations: Heterogeneous study designs and operationalisations of insight precluded a meta-analytic summary. Publication bias and selective reporting is possible, given insight was typically not a primary outcome of the included studies.
Keywords: Insight; Mental health; Mystical experience; Psychedelics; Well-being.
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