A systematic review of longitudinal studies investigating the impact of cannabis use in patients with psychotic disorders

ABSTRACT

Introduction: Research has established a link between cannabis use and adverse psychotic outcomes in psychosis patients. However, we have yet to determine if this relationship is maintained when controlling for important confounding variables. The following systematic review aims to investigate if the association between cannabis use and psychotic outcomes is preserved when accounting for important confounders, and if discontinued use mitigates any potential negative impacts.

Areas covered: The authors conducted an exhaustive search of the MEDLINE database and Google Scholar to identify articles pertaining to the systematic review. Thirty-three articles were retained for meeting the eligibility criteria.

Expert opinion: The evidence confirms an overarching pattern of negative psychotic outcomes of cannabis intake in psychosis populations, even when accounting for crucial confounders. Psychosis patients should be informed with evidence-based health information regarding the effects of cannabis use. Clinicians should systematically evaluate cannabis intake patterns in psychosis patients and offer intervention services geared toward reducing problematic consumption. Researchers should record confounding factors in a more systematic manner in future longitudinal investigations while paying careful attention to the potency and dose–response effects of the ingested cannabis. Deciders will need to investigate the impact of cannabis regulations on psychosis populations.

KEYWORDS:

• Cannabis
• longitudinal
• psychosis
• relapse
• review

Supplementary material

Supplemental data for this article can be accessed here.

Article highlights

• Cannabis intake is associated with worse psychotic outcomes (rehospitalisation or change in positive symptoms) in psychosis populations

• The negative impact of cannabis is maintained even when controlling for important mitigating factors such as other substance use

• Future efforts must be placed in clinical settings to address problematic cannabis use, such as the dissemination of information regarding the adverse health effects of cannabis on psychosis prognosis, the benefits of discontinued use, as well as the provision of interventions aiming at reduction, cessation, or safer use (harm reduction) of cannabis

• Further research must be conducted to investigate cannabis potency and dose–response effects in populations with psychosis, and systematically address potential mitigating factors such as medication compliance.

Reviewer disclosures

Peer reviewers in this manuscript have no relevant financial or other relationships to disclose.

Acknowledgements

A Dumais is the holder of a Junior II Investigator award from the Fonds de Recherche du Québec en Santé. D Jutras-Aswad is holder of an investigator award from the Fonds de Recherche du Québec en Santé. M Athanassiou is holder of a PhD scholarship from the Fonds de Recherche du Québec en Santé. S Potvin is holder of the Eli Lilly Canada Chair on schizophrenia research.

Declaration of interest

A Abdel-Baki has received speaker fees and research grants from Janssen-Orthto Inc.  The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or conflict with the subject matter or materials discussed in this manuscript apart from those disclosed.

Additional information

Funding

This paper was not funded.