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.

Download full-text


Available from: Theresa Helen Mazarello Moore,
  • Source
    • "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). "
    [Show abstract] [Hide abstract]
    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.
    12/2015; 2:53-56. DOI:10.1016/j.pmedr.2014.12.006
    • "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). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Media reports suggest increasing popularity of marijuana concentrates ("dabs"; "earwax"; "budder"; "shatter; "butane hash oil") that are typically vaporized and inhaled via a bong, vaporizer or electronic cigarette. However, data on the epidemiology of marijuana concentrate use remain limited. This study aims to explore Twitter data on marijuana concentrate use in the U.S. and identify differences across regions of the country with varying cannabis legalization policies. Tweets were collected between October 20 and December 20, 2014, using Twitter's streaming API. Twitter data filtering framework was available through the eDrugTrends platform. Raw and adjusted percentages of dabs-related tweets per state were calculated. A permutation test was used to examine differences in the adjusted percentages of dabs-related tweets among U.S. states with different cannabis legalization policies. eDrugTrends collected a total of 125,255 tweets. Almost 22% (n=27,018) of these tweets contained identifiable state-level geolocation information. Dabs-related tweet volume for each state was adjusted using a general sample of tweets to account for different levels of overall tweeting activity for each state. Adjusted percentages of dabs-related tweets were highest in states that allowed recreational and/or medicinal cannabis use and lowest in states that have not passed medical cannabis use laws. The differences were statistically significant. Twitter data suggest greater popularity of dabs in the states that legalized recreational and/or medical use of cannabis. The study provides new information on the epidemiology of marijuana concentrate use and contributes to the emerging field of social media analysis for drug abuse research. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
    Drug and alcohol dependence 08/2015; DOI:10.1016/j.drugalcdep.2015.07.1199 · 3.42 Impact Factor
    • "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). "
    [Show abstract] [Hide abstract]
    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; 168(1). DOI:10.1016/j.schres.2015.07.051 · 3.92 Impact Factor
Show more