We conducted a systematic review of meta-analyses and systematic reviews to evaluate the impact of cannabis use on the onset and course of psychoses. Following a systematic literature search of five data bases (2005–2016) and consecutive structured evaluation, we were able to include 26 systematic reviews and meta-analyses. The methodological quality of the included publications were in the range of high and poor. The scientific literature indicates that psychotic illness arises more frequently in cannabis users compared to non-users, cannabis use is associated with a dose-dependent risk of developing psychotic illness, and cannabis users have an earlier onset of psychotic illness compared to non-users. Cannabis use was also associated with increased relapse rates, more hospitalizations and pronounced positive symptoms in psychotic patients. We make recommendations about the type of research that is required to better characterize the relationship between cannabis use and the development and outcomes of psychosis.
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We acknowledge the contribution of Johannes Kabisch, Kathrin Schacherbauer, Luise Jacob, Sophia Schmieder, Udo Bonnet, Jan Copeland, Marica Ferri, Christopher Fowler, Winfried Häuser, Derik Hermann, Burkhard Hinz, Michael Höfler, Joseph Kambeitz, Ludwig Kraus, Beat Lutz, Frank Petzke, Liane Paul, Lukas Radbruch, Martin Storr, Michael Schäfer.
This paper was prepared in the context of the study “Cannabis: Potential and risks. A scientific analysis” (PIs: Dr. Eva Hoch, Dr. Miriam Schneider) funded by the German Ministry of Health. The funding sources had no influence on the design of the study or the analysis and interpretation of the results.
Conflict of interest
AH was an advisory board member of Janssen-Cliag, Otsuka, Lundbeck and Roche and he was a speaker for Janssen-Cliag, Otsuka and Lundbeck. FML is a shareholder of curantis UG (ltd.) and has received research grants from the German Federal Ministry of Education and Research and Acerus Pharmaceuticals. EH received research grants from the German Federal Ministry of Health and the European Monitoring Centre for Drugs and Drug Addiction. She receives fees for trainings and a treatment manual for cannabis use disorders. WS received speakers fees by Mag & More. All other authors did not report a conflict of interest. All other authors did not report any conflicts of interest related to the content of this article.
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Hasan, A., von Keller, R., Friemel, C.M. et al. Cannabis use and psychosis: a review of reviews. Eur Arch Psychiatry Clin Neurosci 270, 403–412 (2020). https://doi.org/10.1007/s00406-019-01068-z
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