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Abstract
Introduction: Cannabis is the most consumed illicit substance in Europe. Although its sale and use remain generally prohibited, European public policies have evolved in recent years by legalizing cannabis for medical use and considering its legalization for recreational use. However, in the literature there are arguments in favor of a particular relationship between cannabis consumption and the development of psychotic symptoms. Thus, since cannabis consumption tends to increase with legalization, the aim of this review was to investigate the impact of the legalization of cannabis for recreational use on the risk of psychosis in regions of the world already concerned.
Method: A systematic review of the literature was carried out in April 2024 in the PubMed-Medline database according to PRISMA criteria. The sequence of keywords used was as follows: (“Cannabis” [Mesh] or cannabis) AND ((“Psychotic Disorders” [Mesh] or Psychotic Disorders) or (“Schizophrenia Spectrum and Other Psychotic Disorders” [Mesh]) or (“Schizophrenia” [Mesh] or Schizophrenia)) AND legal use. The inclusion criteria applied for the selection of articles in this systematic review were: (1) any article investigating the potential impact of the legalization of cannabis for recreational use on the risk of psychosis (any type of psychosis diagnosed according to ICD-9, ICD-10, DSM-4 or DSM-5) by the intermediary of epidemiological (incidence or prevalence) and/or clinical (ambulatory consultations, emergency visits or hospitalizations) criteria, (2) any type of study (cross-sectional, longitudinal, prospective, retrospective, interventional and experimental) with a methodology including a temporal and/or geographic comparison of the risk of psychosis associated with the legalization of cannabis for recreational use with the exception of literature reviews and clinical cases descriptions, (3) absence of limitation for the age of the populations studied and for the date of publication, and (4) articles written in English or French. After evaluation by the two authors of the 160 articles identified, seven studies investigating the impact of the legalization of cannabis for recreational use on the risk of psychosis were included in this systematic literature review.
Results: Four of the studies showed no increase in the use of health services for psychosis following the legalization of cannabis for recreational use whereas three other studies highlighted a negative impact of the legalization of cannabis for recreational use on the risk of psychosis. All of these studies were carried out in North America and were characterized by a low level of scientific evidence.
Conclusion: Given the complexity of assessing the impact of the legalization of cannabis for recreational use on the risk of psychosis, additional investigations through studies of better scientific quality are essential. However, based on the data already available, there is some evidence that there is a potential negative impact on mental health due to the legalization of cannabis for recreational use. In this context, in the event of legalization of cannabis for recreational use it seems essential to recommend lower risk use of cannabis (limit the frequency of use, delay the age of first consumption, control the THC content of products and promote prevention/education). Finally, in order to enable dynamic evolution of public health strategies the establishment of continued monitoring is essential as cannabis legalization evolves.