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Cannabis and psychosis: the impact of polydrug use

Mark Shevlin (Psychology Research Institute, School of Psychology, Ulster University, Derry, UK)
Eoin McElroy (Psychology Research Institute, School of Psychology, Ulster University, Derry, UK)
Jamie Murphy (Psychology Research Institute, School of Psychology, Ulster University, Derry, UK)
Philip Hyland (National College of Ireland, Dublin, Ireland) (School of Psychology, Centre for Global Health, Trinity College Dublin, Ireland)
Frédérique Vallieres (School of Psychology, Centre for Global Health, Trinity College Dublin, Ireland)
Ask Elklit (National Centre for Psychotraumatology, Institute for Psychology, University of Southern Denmark, Odense, Denmark)
Mogens Christoffersen (Danish National Centre for Social Research, Copenhagen, Denmark)

Drugs and Alcohol Today

ISSN: 1745-9265

Publication date: 4 September 2017

Abstract

Purpose

While research has consistently identified an association between cannabis use and psychosis, few studies have examined this relationship in a polydrug context (i.e. combining cannabis with other illicit substances). The paper aims to discuss this issue.

Design/methodology/approach

The present study sought to examine the association between recreational drug use (cannabis only vs polydrug) and psychotic disorders. Analysis was conducted on a large, representative survey of young Danish people aged 24 (n=4,718). Participants completed self-report measures of lifetime drug use and this information was linked to the Danish psychiatric registry system.

Findings

Multivariate binary logistic regression analysis was used to examine the association between drug use (no drug use, cannabis only, cannabis and other drug) and ICD-10 psychotic disorders, while controlling for gender and parental history of psychosis. Compared with no drug use, the use of cannabis only did not increase the risk of psychosis while the odds ratio for cannabis and other drug were statistically significant.

Research limitations/implications

Psychosis risk may be associated with the cumulative effect of polydrug use.

Practical implications

Cannabis use may be a proxy for other drug use in research studies.

Originality/value

This study is innovative as it uses linked self-report and administrative data for a large sample. Administrative data were used to as an objective mental health status indicator.

Keywords

Acknowledgements

The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committee on human experimentation with the Helsinki Declaration of 1975, as revised in 2008. The authors assert that ethical approval for publication of this audit has been provided by their local REC. This research received no specific grant from any funding agency, commercial or not-for-profit sectors.

Citation

Shevlin, M., McElroy, E., Murphy, J., Hyland, P., Vallieres, F., Elklit, A. and Christoffersen, M. (2017), "Cannabis and psychosis: the impact of polydrug use", Drugs and Alcohol Today, Vol. 17 No. 3, pp. 186-194. https://doi.org/10.1108/DAT-03-2017-0014

Publisher

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Emerald Publishing Limited

Copyright © 2017, Emerald Publishing Limited