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


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
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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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    ABSTRACT: Objective: Although cannabis is an illegal drug, 'medical marijuana programs' (MMPs) have proliferated (e.g., in Canada and several US states), allowing for legal cannabis use for therapeutic purposes. While both health risks and potential therapeutic benefits for cannabis use have been documented, potential public health impacts of MMPs - also vis-à-vis other psychoactive substance use - remain under-explored. Methods: We briefly reviewed the emerging evidence on MMP participants' health status, and specifically other psychoactive substance use behaviors and outcomes. Results: While data are limited in amount and quality, MMP participants report improvements in overall health status, and specifically reductions in levels of risky alcohol, prescription drug and - to some extent - tobacco or other illicit drug use; at the same time, increases in cannabis use and risk/problem patterns may occur. Conclusion: MMP participation may positively impact - for example, by way of possible 'substitution effects' from cannabis use - other psychoactive substance use and risk patterns at a scale relevant for public health, also influenced by the increasing population coverage of MMPs. Yet, net overall MMP-related population health effects need to be more rigorously and comprehensively assessed, including potential increases in cannabis use related risks and harms.
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    • "Most commonly, they are vaporized and inhaled via a bong, oil pipe, vaporizer or electronic cigarette (Loflin and Earleywine, 2014; DEA, 2014b). Because of the increased THC concentration and novel means of administration, use of " dabs " might lead to more severe psychological and physical problems, (Moore et al., 2007; Hall and Degenhardt, 2009; Degenhardt et al., 2013). Prior research has suggested that use of high potency cannabis may increase the risk of cannabis dependence (Hall and Degenhardt, 2015), first-episode psychosis (Di Forti et al., 2014, 2015), and contribute to the cognitive skills impairment (Ramaekers et al., 2006). "
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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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    ABSTRACT: Cannabis has been suggested to impair the capacity to recognize discrepancies between expected and executed actions. However, there is a lack of conclusive evidence regarding the acute impact of cannabis on the neural correlates of error monitoring. In order to contribute to the available knowledge, we used a randomized, double-blind, between-groups design to investigate the impact of administration of a low (5.5 mg THC) or high (22 mg THC) dose of vaporized cannabis vs. placebo on the amplitudes of the error-related negativity (ERN) and error positivity (Pe) in the context of the Flanker task, in a group of frequent cannabis users (required to use cannabis minimally 4 times a week, for at least 2 years). Subjects in the high dose group (n =18) demonstrated a significantly diminished ERN in comparison to the placebo condition (n =19), whereas a reduced Pe amplitude was observed in both the high and low dose (n=18) conditions, as compared to placebo. The results suggest that a high dose of cannabis may affect the neural correlates of both the conscious (late), as well as the initial automatic processes involved in error monitoring, while a low dose of cannabis might impact only the conscious (late) processing of errors.
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