Article

Cannabis use and risk of psychotic or affective mental health outcomes: A systematic review

Academic Unit of Psychiatry, University of Bristol, Bristol, UK.
The Lancet (Impact Factor: 45.22). 08/2007; 370(9584):319-28. DOI: 10.1016/S0140-6736(07)61162-3
Source: PubMed

ABSTRACT Whether cannabis can cause psychotic or affective symptoms that persist beyond transient intoxication is unclear. We systematically reviewed the evidence pertaining to cannabis use and occurrence of psychotic or affective mental health outcomes.
We searched Medline, Embase, CINAHL, PsycINFO, ISI Web of Knowledge, ISI Proceedings, ZETOC, BIOSIS, LILACS, and MEDCARIB from their inception to September, 2006, searched reference lists of studies selected for inclusion, and contacted experts. Studies were included if longitudinal and population based. 35 studies from 4804 references were included. Data extraction and quality assessment were done independently and in duplicate.
There was an increased risk of any psychotic outcome in individuals who had ever used cannabis (pooled adjusted odds ratio=1.41, 95% CI 1.20-1.65). Findings were consistent with a dose-response effect, with greater risk in people who used cannabis most frequently (2.09, 1.54-2.84). Results of analyses restricted to studies of more clinically relevant psychotic disorders were similar. Depression, suicidal thoughts, and anxiety outcomes were examined separately. Findings for these outcomes were less consistent, and fewer attempts were made to address non-causal explanations, than for psychosis. A substantial confounding effect was present for both psychotic and affective outcomes.
The evidence is consistent with the view that cannabis increases risk of psychotic outcomes independently of confounding and transient intoxication effects, although evidence for affective outcomes is less strong. The uncertainty about whether cannabis causes psychosis is unlikely to be resolved by further longitudinal studies such as those reviewed here. However, we conclude that there is now sufficient evidence to warn young people that using cannabis could increase their risk of developing a psychotic illness later in life.

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Available from: Theresa Helen Mazarello Moore, Aug 22, 2015
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    • "Despite cannabis increasing the risk of developing psychosis in vulnerable individuals (Moore et al., 2007), use is common in individuals with a psychotic disorder (Morgan et al., 2010). In non-clinical individuals, cannabis use is associated with widespread neurocognitive deficits similar to impairments in schizophrenia, including compromised attention, memory and executive functioning (Thames et al., 2014). "
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    • "). Delta-9-tetrahydrocannabinol (THC), the main psychoactive cannabinoid present in the plant, has been found to evoke most of the subjective effects of marijuana (Grotenhermen, 2003). Around 20% of young people worldwide abuse the psychoactive effects of THC and other cannabinoids through regular use of the cannabis plant (Moore et al., 2007). This makes it important to understand whether and how cannabis intoxication affects human information processing. "
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    • "Other risk factors for cannabis dependence that were identified in general population studies include a family history of substance use disorders, parents' marital problems, early life events, impulsivity, aggressive or delinquent behaviour, and the presence of externalising disorders (Bruns and Geist, 1984; Coffey et al., 2002; Fergusson et al., 2007; Florez-Salamanca et al., 2013; Hayatbakhsh et al., 2006, 2009; Hyman and Sinha, 2009; Lopez-Quintero et al., 2010; Perkonigg et al., 2008; Pingault et al., 2012; Swift et al., 2008; Von Sydow et al., 2002; Wittchen et al., 2007). The role of internalising disorders is still unclear (Moore et al., 2007). Yet, there is increasing evidence for an association between mood/anxiety disorders and heavy or problematic cannabis use (Degenhardt et al., 2003). "
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