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

Abstract

Background Cannabis use is associated with increased risk of later psychotic disorder but whether it affects incidence of the disorder remains unclear. We aimed to identify patterns of cannabis use with the strongest effect on odds of psychotic disorder across Europe and explore whether differences in such patterns contribute to variations in the incidence rates of psychotic disorder. Methods We included patients aged 18-64 years who presented to psychiatric services in 11 sites across Europe and Brazil with first-episode psychosis and recruited controls representative of the local populations. We applied adjusted logistic regression models to the data to estimate which patterns of cannabis use carried the highest odds for psychotic disorder. Using Europe-wide and national data on the expected concentration of Δ⁹-tetrahydrocannabinol (THC) in the different types of cannabis available across the sites, we divided the types of cannabis used by participants into two categories: low potency (THC <10%) and high potency (THC ≥10%). Assuming causality, we calculated the population attributable fractions (PAFs) for the patterns of cannabis use associated with the highest odds of psychosis and the correlation between such patterns and the incidence rates for psychotic disorder across the study sites. Findings Between May 1, 2010, and April 1, 2015, we obtained data from 901 patients with first-episode psychosis across 11 sites and 1237 population controls from those same sites. Daily cannabis use was associated with increased odds of psychotic disorder compared with never users (adjusted odds ratio [OR] 3•2, 95% CI 2•2-4•1), increasing to nearly five-times increased odds for daily use of high-potency types of cannabis (4•8, 2•5-6•3). The PAFs calculated indicated that if high-potency cannabis were no longer available, 12•2% (95% CI 3•0-16•1) of cases of first-episode psychosis could be prevented across the 11 sites, rising to 30•3% (15•2-40•0) in London and 50•3% (27•4-66•0) in Amsterdam. The adjusted incident rates for psychotic disorder were positively correlated with the prevalence in controls across the 11 sites of use of high-potency cannabis (r = 0•7; p=0•0286) and daily use (r = 0•8; p=0•0109). Interpretation Differences in frequency of daily cannabis use and in use of high-potency cannabis contributed to the striking variation in the incidence of psychotic disorder across the 11 studied sites. Given the increasing availability of high-potency cannabis, this has important implications for public health.

The independent and combined influence of schizophrenia polygenic risk score and heavy cannabis use on risk for psychotic disorder: A case-control analysis from the EUGEI study.

“…Data on patterns of cannabis use were collected using the modified Cannabis Experience Questionnaire further updated (CEQ EU-GEI ) 7 . None of the materials we used for the participants recruitment referred to cannabis or to its potential role as a risk factor for psychotic disorder.…”

“…Prospective epidemiological studies 4 , as well as biological investigations 5 , demonstrate a causal link between cannabis use and psychotic disorder. Recent evidence has confirmed a) a dose-response association with the highest odds of psychotic disorder in the heaviest cannabis users 6 and b) that high potency cannabis carries the greatest risk for psychotic disorder 7 . Indeed, daily cannabis use and use of high potency types have been linked to variation in the incidence of psychotic disorder across Europe 6 .…”

Psychotic disorders hospitalizations associated with cannabis abuse or dependence: A nationwide big data analysis

“…Patients diagnosed with a first episode of psychosis or with schizophrenia are more likely to report current or prior use of cannabis, compared with the general population. Cannabis properties also play a role with the incidence of a first psychotic event being linked to the dosage of the cannabis used by the patient (Andreasson, Allebeck, Engstrom, & Rydberg, 1987;Di Forti et al, 2019;Roncero et al, 2018;Zammit, Allebeck, Andreasson, Lundberg, & Lewis, 2002). Continued CU not only might play a role on the first psychotic event but also affects negatively the prognosis of a patient after the first episode of psychosis, increasing the relapse rate (Schoeler et al, 2016).…”

Adolescent cannabis use and risk of mental health problems—the need for newer data

“…For example, a recent meta‐analysis regarding cannabis and risk of psychosis included numerous studies measuring cannabis use in the 20th century, including the landmark study of Swedish conscripts evaluated in 1969–1970 . This is concerning given new research suggesting that using high‐potency cannabis increases risk of psychotic disorder significantly more than low‐potency cannabis .…”