Research paper
A literature review and meta-analyses of cannabis use and suicidality

https://doi.org/10.1016/j.jad.2016.02.007Get rights and content

Highlights

  • We lack evidence that acute cannabis use increases imminent risk for suicidality.

  • While chronic cannabis use can predict suicidality limitations are noted.

  • We found heterogeneity on cannabis exposure and control of confounding.

  • Research on women who use cannabis is more limited and a matter of great urgency.

Abstract

Background

We lack a review of the epidemiological literature on cannabis use (acute use and chronic-usual quantity/frequency and heavy use) and suicidality (suicide death, suicide ideation, suicide attempt).

Methods

The English language literature on Medline, PsychInfo, Google Scholar, and public-use databases was searched for original articles, critical review reports, and public use data on cannabis use and suicide for the period ranging from 1990–2015 (February). Odds ratios (OR) from random effects in meta-analyses for any cannabis use and heavy cannabis use were calculated.

Results

The acute cannabis-suicidality literature mostly includes descriptive toxicology reports. In terms of death by suicide, the average positive cannabis rate was 9.50% for studies sampling from all suicides, with higher cannabis detection rates amongst suicide decedents by non-overdose methods. We found only 4 studies providing estimates for any chronic cannabis use and death by suicide (OR=2.56 (1.25–5.27)). After deleting duplicates we found 6 studies on any cannabis use and suicide ideation (OR=1.43 (1.13–1.83)), 5 studies on heavy cannabis use and suicide ideation (OR=2.53 (1.00–6.39)), 6 studies on any cannabis use and suicide attempt (OR=2.23 (1.24–4.00)) and 6 studies on heavy cannabis use and suicide attempt (OR=3.20 (1.72–5.94)).

Conclusions

We currently lack evidence that acute cannabis use increases imminent risk for suicidality. The evidence tends to support that chronic cannabis use can predict suicidality, but the lack of homogeneity in the measurement of cannabis exposure and, in some instances, the lack of systematic control for known risk factors tempered this finding.

Introduction

The last report from the Institute for Health Metrics and Evaluation (IHME), Global Burden of Disease (GBD) group on the burden of mental and substance use disorders on deaths by suicide (Ferrari et al., 2014), did not include cannabis dependence as a risk factor for suicide. Another update from the GDB study group (Hall and Degenhardt, 2014), that included 2 new studies and another review paper (Moore et al., 2007), considered this association somehow contradictory and possibly biased. These reviews tend to include suicidal behavior (i.e., death by suicide and non-fatal suicide attempts) as part of mental health consequences of cannabis use and plainly disregard the cannabis-suicidal behavior association. A current international report on suicide (World Health Organization, 2014), only briefly mentions an association between cannabis dependence and suicide. We believe that a separation of outcomes (suicidal ideation, attempt and death; hereby referred to as “suicidality”) is needed if we want to understand this phenomenon at a fine-grained level (i.e., to determine specifically where there is indeed a lack of evidence and/or a need for additional studies/analyses in order to determine evidence of an association). Also, while prior reviews acknowledge the limitations of what is considered cannabis/marijuana exposure (any use, frequency of regular use, disorders) they all discuss the long-term effects of cannabis exposure. To the best of our knowledge, no review has included an evaluation of a potential short-term, acute triggering effect of cannabis use on suicidal behavior, a matter of potential relevance similar to the acute use of alcohol (Cherpitel et al., 2004, Bagge and Sher, 2008, Bagge and Schumacher, 2010). The possibility of an association between acute and chronic cannabis use and suicidality is relevant because cannabis use and cannabis use disorders are amongst the most common form of illicit substance use and illicit substance use disorders worldwide (Degenhardt et al., 2008, Degenhardt and Hall, 2012), and its role on suicidality could potentially have implications for the calculations of the burden of disease.

A new review suggested possible mechanisms for cannabis use to have an effect on suicidality, including causal effects, reverse causation, correlated liabilities and by triggering effects (Agrawal and Lynskey, 2014). Cross-sectional analyses based on community-based twin samples have found modest associations between cannabis use with suicide ideation and unplanned suicide attempts (Delforterie et al., 2015) adjusting for psychiatric disorders and substance involvement. We currently lack an overall evaluation of the potential cannabis-suicidality association using a fine-grained approach and, most importantly, recommendations are needed to (1) best determine whether this relation exists and to (2) responsibly respond to the public debate on the topic. Given the above limitations of prior reviews, we will provide an updated (1990–[1995 for acute use] up to February 2015) revision of the epidemiological literature on acute and chronic effects of cannabis on suicidality, with discussions on suicidal ideation, attempts and deaths.

Section snippets

Methods

Our approach to understanding the cannabis-suicidality relation closely models a set of reviews (Hufford, 2001, Cherpitel et al., 2004, Borges and Loera, 2010), and a conceptual framework (Bagge and Sher, 2008), distinguishing between acute and chronic use of alcohol in their relations with suicidality.

For this review, the English language literature on Medline, PsychInfo, Google Scholar, and public-use databases (e.g., Substance Abuse and Mental Health Services Administration) was searched for

Suicidal ideation and attempt

To our knowledge, only one study exists which hints at the possibility that acute cannabis use can induce suicidal ideation. A case study (Raja and Azzoni, 2009), describes a patient who presented to the emergency department (ED) with suicidal ideation (and urge to attempt suicide by fall), anxiety, and agitation after smoking cannabis use a few hours prior.

The Drug Abuse Warning Network DAWN (Subtance Abuse And Mental Health Services Administration, 2011), provides 2011 national US estimates

Overall summary and limitations of acute cannabis-suicidality relations

The acute cannabis-suicidal ideation and behavior literature is small and spans multiple countries. It mostly includes case-series and descriptive toxicology reports, and only a handful of studies include a between-subject control group, or a within-subject control period that provide essential information regarding whether an association exists. The vast majority of studies reviewed use toxicology tests where a positive test can indicate last use which was weeks prior to suicidal behavior.

Acknowledgments

This work was done while Guilherme Borges was on a consultancy for the Management of Substance Abuse (MSB), Department of Mental Health and Substance Abuse (MSD)-World Health Organization (Geneva- Switzerland)-A presentation of an initial version of this manuscript was done at the World Health Organization (WHO) Scientific meeting on harms to health due to cannabis use- Stockholm, Sweden, villa aske, bro, 21–23 April 2015.

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