S92. REASONS TO START SMOKING CANNABIS: A CASE CONTROL-ANALYSIS FROM THE EUGEI STUDY
Authors: Spinazzola Edoardo , Rodriguez Victoria , Quattrone Diego , Trotta Giulia , Di Forti Marta , Murray Robin 
Published: May 2020

Background

Studies have shown that cannabis can increase the risk of psychosis from 1.7 to 3.9 times. Both frequency and potency seem to contribute to differences in the incidence of psychosis across Europe. Despite this evidence, sceptics argue that that the association between cannabis use and psychotic disorders could be explained by: (a) subjects who start experiencing psychosis use cannabis as a form of self-medication; (b) the co-morbid effect of other psychotogenic drugs (e.g., amphetamines); or (c) there is a common genetic vulnerability between cannabis use and psychosis. Thus, we aim to analyse: 1) reported reasons to start using cannabis, 2) if these predict differences in patterns of use (frequency and potency), 3) the association of both reasons to start and pattern of use with PRS for Schizophrenia, as it can explain whether patients with a higher genetic burden also start smoking cannabis after experiencing a higher psychological discomfort.

Methods

Using data from the multicentric EUGEI First-Episode Psychosis (FEP) case-control study we examined differences in reasons to start using cannabis between cases and controls. Data were obtained from the Cannabis Experiences Questionnaire modified version. Logistic regression models were used to test if reason to start predicted different patterns of use. Finally, we used regression to test if Polygenic risk scores for schizophrenia (SZ PRS) explained variance in reasons to start.

Results

Up to 85% of controls compared to 68% of FEP started using cannabis because either friends or family were using it. Instead, 18% of cases started using cannabis to feel better compared 5% of controls, reporting the 13.4% of cases and 10.3% of controls having start due to “other reasons”. Regression models showed that being a case was positively associated with starting use in order to feel better (RRR 4.67, z=7.58, p&lt;0.001), remaining significant after adjusting for gender, age, ethnicity or site. We did not find evidence of an association between start using cannabis “to feel better” and potency nor in cases or controls. We found an association for both cases and controls between those who started smoking to feel better and the frequency of use following a gradient from “more than once a week” to “daily”. Using cannabis “to feel better” was associated with a 4 times increase in the risk (RRR=4.45 95% CI 1.85 – 10.72) of using it daily in controls and 3 times increase (RRR= 3.11 95% CI 1.81 – 5.35) in FEP. Multinomial regression showed that reasons to start did not change according to Schizophrenia PRS, with those starting because a family member was using cannabis (RRR =1 95% CI 0.38 – 2.62) and those starting to feel better (RRR = 1.05 95% CI 0.47 – 2.33) not being at higher polygenic risk compared with those starting because their friends were using cannabis.

Discussion

These preliminary findings show that a higher proportion of patients with psychosis than controls start using cannabis as a way to make them feel better, although they are a minority. Furthermore, both cases and controls that started smoking “to feel better” presented higher chances to start smoking more frequently. Lastly, PRS did not predict the reasons to start smoking cannabis.