Article

Moore TH, Zammit S, Lingford-Hughes A, Barnes TR, Jones PB, Burke M et al. Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review. Lancet 370: 319-328

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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    • "For example, cannabis (Gordon et al., 2013; Room et al., 2010; Volkow et al., 2014; Hall and Degenhardt, 2009) may entail various acute cognitive , memory and/or psychomotor impairments (Crean et al., 2011) specifically associated with elevated risk for (e.g., motor-vehicle) accidents or injury. Cannabis use furthermore brings risk for both dependence and psychotic and/or depression problems (Moore et al., 2007), and is associated with the incidence of different forms of (e.g., lung) cancers (Mehra et al., 2006; Zhang et al., 1999); moreover, cannabis use commonly results in other pulmonary and bronchial problems (Tetrault et al., 2007). Importantly for public health, intensive, frequent or chronic users are at highest risk for most of the above problems (see Degenhardt et al., 2013; Fischer et al., 2011; Hall and Pacula, 2003; Volkow 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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