Review
The blind men and the elephant: Systematic review of systematic reviews of cannabis use related health harms

https://doi.org/10.1016/j.euroneuro.2020.02.003Get rights and content

Highlights

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    Cannabis-related harm is mainly due to mental health consequences.

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    Organic/somatic affectation and associated injury implication are also relevant consequences.

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    Risky use of cannabis should be defined based on frequency and quantity, with a public health perspective.

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    This definition should inform and then evaluate current approaches to a regulated cannabis market.

Abstract

Cannabis is the third most used psychoactive substance worldwide. The legal status of cannabis is changing in many Western countries, while we have very limited knowledge of the public health impact of cannabis-related harms. There is a need for a summary of the evidence of harms and risks attributed to cannabis use, in order to inform the definition of cannabis risky use. We have conducted a systematic review of systematic reviews, aiming to define cannabis-related harms. We included systematic reviews published until July 2018 from six different databases and following the PRISMA guidelines. To assess study quality we applied the AMSTAR 2 tool. A total of 44 systematic reviews, including 1,053 different studies, were eligible for inclusion. Harm was categorized in three dimensions: mental health, somatic harm and physical injury (including mortality). Evidence shows a clear association between cannabis use and psychosis, affective disorders, anxiety, sleep disorders, cognitive failures, respiratory adverse events, cancer, cardiovascular outcomes, and gastrointestinal disorders. Moreover, cannabis use is a risk factor for motor vehicle collision, suicidal behavior and partner and child violence. Cannabis use is a risk factor for several medical conditions and negative social consequences. There is still little data on the dose-dependency of these effects; evidence that is essential in order to define, from a public health perspective, what can be considered risky use of cannabis. This definition should be based on quantitative and qualitative criteria that informs and permits the evaluation of current approaches to a regulated cannabis market.

Introduction

Cannabis is the third most prevalent psychoactive substance worldwide, only after alcohol and tobacco. The annual global estimated prevalence of cannabis use, during the last 12 months, is about 3.9%, meaning that a total of approximately 192 million people aged between 15 and 64 years have used cannabis in 2016 (United Nations Office on Drugs and Crime, 2018).

Cannabis legislative frameworks are evolving worldwide. As of November 2017, medical use, and consequently, production and sale of cannabis is allowed in Australia, Canada, Chile, Colombia, Germany, Israel, Jamaica, The Netherlands, Peru, and in 29 US states (Abuhasira et al, 2018). The recreational use of cannabis has been approved in eight states of the USA, plus the District of Columbia, Uruguay and Canada, which means that new frameworks for controlling the production, distribution and sale of cannabis have been put in place (Government of Canada, 2018). In countries like Spain, Belgium and The Netherlands, cannabis has an ambiguous legal situation and laws concerning production, distribution and sale are not settled yet (United Nations Office on Drugs and Crime, 2018).

These legal changes reflect in part a social perception of decreased risks associated to cannabis (United Nations Office of Drugs and Crime, 2017). In Western countries, and regardless of its legal situation, risk perception of cannabis use is closer to that of alcohol and tobacco than to illicit drugs such as cocaine or heroin. This could contribute to higher cannabis use prevalence (Parker and Anthony, 2018) and in fact, the prevalence of cannabis use in these countries is much closer to alcohol and tobacco than to illegal drugs (United Nations Office on Drugs and Crime, 2018).

Such high prevalence and low social risk perception point to the need to develop secondary prevention strategies aiming at the early identification of risky cannabis users (Casajuana et al., 2016). However, an appropriate identification of ‘risky use’ is still needed, since the literature on the harms associated to cannabis use is scarce and often inconclusive, not discriminating for instance between different types of marijuana (mixed delta-9THC/cannabidiol, mixtures from “skunk”). Narrative and systematic reviews have been conducted on several dimensions of cannabis related harm (Hall, 2015; “WHO | Cannabis,” 2010). More specifically, the American Academies of Science report summarizes the evidence regarding multiple health effects of cannabis and cannabinoid use (National Academies of Sciences, Engineering, 2017). Nevertheless, a global view from a public health perspective is still lacking (Fischer et al/, n.d.).

Hence, the aim of this work is to systematically review all systematic reviews on cannabis related harms, as a first step in the assessment of global risks associated to cannabis use, which in the end should inform the definition of cannabis risky use.

Section snippets

Experimental procedures

This systematic review was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Liberati et al., 2009). This protocol provides a checklist for reporting systematic reviews (Table 1). The study protocol was registered with PROSPERO (registration number: CRD42018089130).

Results

We found 6,725 unique entries of systematic reviews and meta-analyses. Finally, 44 publications were included (Fig. 1). The results of the quality assessment indicated an AMSTAR 2 average of 60.1% affirmative punctuation.

The six dimensions previously included for the search strategy resulted in three domains: 1) mental health (Table 2); 2) somatic (Table 3); 3) injury and mortality (Table 4). Main results are synthesized in Table 5.

Discussion

This systematic review aimed to identify the impact of cannabis use on different health outcomes in order to generate a global picture of cannabis-related harms. We identified 44 systematic reviews, which included 1,053 articles covering a broad spectrum of negative health outcomes directly linked to cannabis use. However, some difficulties arise when pulling together the results.

Frequency and more particularly quantity of cannabis used are usually vaguely defined. More specifically, there is

Funding

This study is funded by the Spanish grant of Plan Nacional Sobre Drogas, Ministerio de Sanidad y Consumo (PNSD 132373 - 2017I053 - 603; Antoni Gual Solé). The conclusions of the article are only the responsibility of the authors and do not necessarily represent the official views of the institutions, who had no further role in study design, collection, analysis and interpretation of the data; in the writing of the paper; or in the decision to submit the paper for publication.

H.L.-P. received

Contributions

MB, AG and HL-P designed the study. EC, HL-P, MB and AG wrote the first draft of the manuscript. All the other authors reviewed and approved the final paper.

Conflict of interest

H.L.-P.: has received travel grants from the laboratories honoraria and travel grants from Janssen and Lundbeck, none of these COI are related to the current research. The other authors declare that they have no known conflicts of interest.

Acknowledgements

CERCA Programme / Generalitat de Catalunya.

Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Hospital Clínic i Universitari de Barcelona.

Plan Nacional Sobre Drogas, Ministerio de Sanidad y Consumo.

Ministry of Economy and Competitiveness, Instituto de Salud Carlos III through a ‘Rıo Hortega’

Janssen and Lundbeck.

References (89)

  • R. Elvik

    Risk of road accident associated with the use of drugs: a systematic review and meta-analysis of evidence from epidemiological studies

    Accid. Anal. Prevent.

    (2013)
  • P.J. Gates et al.

    The effects of cannabinoid administration on sleep: a systematic review of human studies

    Sleep Med. Rev.

    (2014)
  • W. Hall et al.

    Adverse health eff ects of non-medical cannabis use

    Lancet North Am. Ed.

    (2009)
  • J. Duperrouzel et al.

    The association between adolescent cannabis use and anxiety: a parallel process analysis

    Addict. Behav.

    (2018)
  • J.M. Chatkin et al.

    Lung disease associated with marijuana use

    Arch Bronconeumol

    (2017)
  • J.M. Boden et al.

    Modelling possible causality in the associations between unemployment, cannabis use, and alcohol misuse

    Soc. Sci. Med.

    (2017)
  • M.C. Kennedy

    Cannabis: exercise performance and sport. A systematic review

    J. Sci. Med. Sport

    (2017)
  • J.Y. Ko et al.

    Marijuana use during and after pregnancy and association of prenatal use on birth outcomes: a population-based study

    Drug Alcohol Depend.

    (2018)
  • P.-Y. Le Bec et al.

    Cannabis et psychose: recherche d'un lien de causalité à partir d'une revue critique systématique de la littérature

    L'Encéphale

    (2009)
  • J. Macleod et al.

    Psychological and social sequelae of cannabis and other illicit drug use by young people: a systematic review of longitudinal, general population studies

    Lancet North Am. Ed.

    (2004)
  • C. Marangoni et al.

    The role of environmental exposures as risk factors for bipolar disorder: a systematic review of longitudinal studies

    J. Affect. Disord.

    (2016)
  • T.H. Moore et al.

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

    Lancet North Am. Ed.

    (2007)
  • M.A. Parker et al.

    Population-level predictions from cannabis risk perceptions to active cannabis use prevalence in the United States, 1991–2014

    Addict. Behav.

    (2018)
  • A. Petrangelo et al.

    774: Obstetrical and neonatal outcomes in pregnancies affected by cannabis abuse or dependence

    Am. J. Obstet. Gynecol.

    (2018)
  • D. Rasic et al.

    Longitudinal associations of cannabis and illicit drug use with depression, suicidal ideation and suicidal attempts among Nova Scotia high school students

    Drug Alcohol Depend.

    (2013)
  • J. Rehm et al.

    Global burden of disease and injury and economic cost attributable to alcohol use and alcohol-use disorders

    Lancet (London, England)

    (2009)
  • O. Rogeberg

    A meta-analysis of the crash risk of cannabis-positive drivers in culpability studies—avoiding interpretational bias

    Accid. Anal. Prev.

    (2019)
  • I.H. Ruisch et al.

    Maternal substance use during pregnancy and offspring conduct problems: a meta-analysis

    Neurosci. Biobehav. Rev.

    (2018)
  • A. Szoke et al.

    Association between cannabis use and schizotypal dimensions – a meta-analysis of cross-sectional studies

    Psychiatry Res.

    (2014)
  • A. Wettlaufer et al.

    Estimating the harms and costs of cannabis-attributable collisions in the Canadian provinces

    Drug Alcohol Depend.

    (2017)
  • M. Asbridge et al.

    Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis

    BMJ

    (2012)
  • G.Del Balzo et al.

    " Positive " urine testing for Cannabis is associated with increased risk of traffic crashes

    J. Pharm. Biomed. Anal.

    (2018)
  • J. Berthiller et al.

    Cannabis Smoking and Risk of Lung Cancer in Men: A Pooled Analysis of Three Studies in Maghreb

    (2008)
  • S.A. Bradford et al.

    The environment and disease: association or causation?

    Proc. R. Soc. Med.

    (1965)
  • A.J. Budney et al.
    (2019)
  • B. CALABRIA et al.

    Does cannabis use increase the risk of death? Systematic review of epidemiological evidence on adverse effects of cannabis use

    Drug Alcohol Rev.

    (2010)
  • N. Carrigan et al.

    A systematic review of the relationship between psychological disorders or substance use and self-reported cognitive failures

    Cogn. Neuropsychiatry

    (2016)
  • C. Casajuana et al.

    Definitions of risky and problematic cannabis use: a systematic review

    Subst. Use Misuse

    (2016)
  • V. Choenni et al.

    Association between substance use and the perpetration of family violence in industrialized countries

    Trauma, Violence Abuse

    (2017)
  • R.D. Crean et al.
    (2011)
  • A.-K. Danielsson et al.

    Cannabis use among Swedish men in adolescence and the risk of adverse life course outcomes: results from a 20 year-follow-up study

    Addiction

    (2015)
  • M. Di Forti et al.

    The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study

    Lancet Psychiatry

    (2019)
  • J.R. Dugré et al.

    Persistency of cannabis use predicts violence following acute psychiatric discharge

    Front. Psychiatry

    (2017)
  • Fischer, B., Rehm, J., & Hall, W.(n.d.). Cannabis use in Canada: the need for a “public health” approach. Can. J....

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