Assessing evidence for a causal link between cannabis and psychosis: a review of cohort studies.
Jennifer McLaren, Edmund Silins, D. Hutchinson, R. Mattick, W. Hall
The International journal on drug policy 2010 DOI: 10.1016/j.drugpo.2009.09.001 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Systematic review Peer reviewed |
|---|---|
| Population | General population cohorts |
| Topics | Cannabis |
| Key findings | The authors argue that although the reviewed cohort studies support criteria for a causal association between cannabis use and psychosis, methodological limitations in measuring psychosis, intoxication, confounders, and follow-up drug use mean the data cannot determine whether cannabis causes serious psychotic disorders that would not otherwise have occurred. Pre-existing vulnerability to psychosis is identified as an important influencing factor. |
Abstract
Over the past five years, the release of cohort studies assessing the link between cannabis and psychosis has increased attention on this relationship. Existing reviews generally conclude that these cohort studies show cannabis has a causal relationship to psychosis, or at least that one cannot be excluded. Few studies have evaluated the relative strengths and limitations of these methodologically heterogeneous cohort studies, and how their relative merits and weaknesses might influence the way the link between cannabis use and psychosis is interpreted. This paper reviews the methodological strengths and limitations of major cohort studies which have looked at the link between cannabis and psychosis, and considers research findings against criteria for causal inference. Cohort studies that assessed the link between cannabis and psychosis were identified through literature searches using relevant search terms and MEDline, PsycINFO and EMBASE. Reference lists of reviews and key studies were hand searched. Only prospective studies of general population cohorts were included. Findings were synthesised narratively. A total of 10 key studies from seven general population cohorts were identified by the search. Limitations were evident in the measurement of psychosis, consideration of the short-term effects of cannabis intoxication, control of potential confounders and the measurement of drug use during the follow-up period. Pre-existing vulnerability to psychosis emerged as an important factor that influences the link between cannabis use and psychosis. Whilst the criteria for causal association between cannabis and psychosis are supported by the studies reviewed, the contentious issue of whether cannabis use can cause serious psychotic disorders that would not otherwise have occurred cannot be answered from the existing data. Further methodologically robust cohort research is proposed and the implications of how evidence informs policy in the case of uncertainty is discussed.
Comparable studies
Other systematic reviews and meta-analyses on cannabis, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Effects of cannabis use on outcomes of psychotic disorders: systematic review People with psychotic disorders, as examined in 13 longitudinal studies | 2008 | Systematic review | |
| The Impact of Cannabis Use on Cognitive Functioning in Patients With Schizophrenia: A Meta-analysis of Existing Findings and New Data in a First-Episode Sample Patients with established schizophrenia (meta-analysis: 572) and patients with... | 2010 | Meta-analysis and cross-sectional observational study | n = 700 |
| Medicinal cannabis for psychiatric disorders: a clinically-focused systematic review | 2020 | Systematic review | |
| Neuroimaging in cannabis use: a systematic review of the literature Cannabis users and controls in neuroimaging studies | 2009 | Systematic review | |
| Human Laboratory Studies on Cannabinoids and Psychosis. Healthy human subjects and individuals with schizophrenia | 2016 | Systematic review |
Citations in the library
Cited by 7
- Investigation of the COMT Val158Met variant association with age of onset of psychosis, adjusting for cannabis use Brain and Behavior October 6, 2017
- Cannabis Use and Clinical Outcomes in First Episode Psychosis: Results From a 2‐Year Follow‐Up Study Early Intervention in Psychiatry May 1, 2026
- Phytocannabinoids and schizophrenia: Focus on adolescence as a critical window of enhanced vulnerability and opportunity for treatment. Pharmacological Research December 1, 2021
- Cannabis Use and the Risk for Psychosis and Affective Disorders Journal of dual diagnosis January 2, 2020
- Cannabis consumption and psychosis or schizophrenia development International Journal of Social Psychiatry November 1, 2018
and 2 more in the library
Cites 13
- Causal association between cannabis and psychosis: examination of the evidence The British Journal of Psychiatry January 30, 2004
- Cannabis-induced psychosis and subsequent schizophrenia-spectrum disorders: follow-up study of 535 incident cases The British Journal of Psychiatry November 30, 2005
- A Clinical and Metabolic Study of Acute Intoxication with Cannabis Sativa and its Role in the Model Psychoses Journal of Mental Science October 1, 1958
- Cannabis use and psychotic disorders: an update Drug and Alcohol Review November 30, 2004
- Cannabis abuse and the course of schizophrenia Cambridge University Press eBooks May 27, 2004
and 8 more in the library