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
    • "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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    ABSTRACT: Findings are unclear as to whether cannabis use is associated with better cognitive functioning in individuals with psychosis. To elucidate the association between cannabis use, neurocognition and social cognition in first-episode psychosis (FEP). Secondary data analysis was conducted on data from 133 FEP participants who had enrolled in a randomized controlled trial of a vocational intervention. Participants completed a neurocognitive and social cognitive battery and characteristics of cannabis use were documented (disorder, recency, frequency and dose). Principal axis factor analysis was used to determine the underlying structure of the cognitive batteries. Regression techniques were used to examine cognitive predictors of current cannabis use disorder (CUD), and recency and frequency of cannabis use. Bivariate correlations were used to examine associations between cognition and dose of cannabis consumption. Male gender (p=.037) was the only significant predictor of having a current CUD. Better processing speed (p=.022) and social cognition (p=.039), male gender (p<.001), and fewer negative symptoms (p=.036) predicted recency of cannabis use. Faster processing speed (p=.007) and male gender (p=.006) also predicted frequency of cannabis use. No variables were significantly associated with dose of cannabis consumption. Better social cognition and processing speed abilities predicting recency and frequency of cannabis use are consistent with cannabis users having higher cognitive abilities. A positive relationship between cannabis use and cognition may be the result of more drug taking opportunities in less cognitively impaired individuals with psychosis. Copyright © 2015 Elsevier B.V. All rights reserved.
    Schizophrenia Research 08/2015; DOI:10.1016/j.schres.2015.07.051 · 4.43 Impact Factor
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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.
    European Neuropsychopharmacology 08/2015; DOI:10.1016/j.euroneuro.2015.08.001 · 5.40 Impact Factor
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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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    ABSTRACT: To examine the course and the predictors of the persistence of cannabis dependence. Through cannabis outlets and chain referral, a prospective enriched community cohort of 207 young adults (aged 18-30) with DSM-IV cannabis dependence at baseline (T0) was formed and followed-up after 1.5 (T1) and 3 (T2) years. The presence of cannabis dependence, cannabis-related problems, functional impairment and treatment was assessed using the Composite International Diagnostic Interview (CIDI 3.0) and the Sheehan Disability Scale (SDS). Predictors of persistence were lifetime cannabis abuse and dependence symptoms, cannabis use characteristics, distant vulnerability factors (e.g. childhood adversity, family history of psychological/substance use problems, impulsivity, mental disorders), and proximal stress factors (recent life events, social support). Four groups were distinguished: persistent dependent (DDD: 28.0%), stable non-persistent (DNN: 40.6%), late non-persistent (DDN: 17.9%) and recurrent dependent (DND: 13.5%). At T2, persisters (DDD) reported significantly more (heavy) cannabis use and cannabis problems than non-persisters (DNN/DDN/DND). Treatment seeking for cannabis-related problems was rare, even among persisters (15.5%). The number (OR = 1.23 (1.03-1.48)) and type ('role impairment' OR = 2.85 (1.11-7.31), 'use despite problems' OR = 2.34 (1.15-4.76)) of lifetime cannabis abuse/dependence symptoms were the only independent predictors of persistence with a total explained variance of 8.8%. Persistence of cannabis dependence in the community is low, difficult to predict, and associated with a negative outcome. The substantial proportion of stable non-persisters suggests that screening and monitoring or low-threshold brief interventions may suffice for many non-treatment-seeking cannabis-dependent people. However, those with many lifetime abuse/dependence symptoms may benefit from more intensive interventions. © 2015 S. Karger AG, Basel.
    European Addiction Research 05/2015; 21(6):279-290. DOI:10.1159/000377625 · 2.07 Impact Factor
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