Abstract
Daily use of high-potency cannabis has been reported to carry a high risk for developing a psychotic disorder. However, the evidence is mixed on whether any pattern of cannabis use is associated with a particular symptomatology in first-episode psychosis (FEP) patients. We analysed data from 901 FEP patients and 1235 controls recruited across six countries, as part of the European Network of National Schizophrenia Networks Studying Gene-Environment Interactions (EU-GEI) study. We used item response modelling to estimate two bifactor models, which included general and specific dimensions of psychotic symptoms in patients and psychotic experiences in controls. The associations between these dimensions and cannabis use were evaluated using linear mixed-effects models analyses. In patients, there was a linear relationship between the positive symptom dimension and the extent of lifetime exposure to cannabis, with daily users of high-potency cannabis having the highest score (B = 0.35; 95% CI 0.14-0.56). Moreover, negative symptoms were more common among patients who never used cannabis compared with those with any pattern of use (B = -0.22; 95% CI -0.37 to -0.07). In controls, psychotic experiences were associated with current use of cannabis but not with the extent of lifetime use. Neither patients nor controls presented differences in depressive dimension related to cannabis use. Our findings provide the first large-scale evidence that FEP patients with a history of daily use of high-potency cannabis present with more positive and less negative symptoms, compared with those who never used cannabis or used low-potency types.
Highlights
There is compelling evidence to suggest that cannabis use is associated with psychotic disorders (Marconi, Di Forti, Lewis, Murray, & Vassos, 2016)
Factor loadings of moderate to high magnitude were observed for most items on the general psychotic experience dimension, whereas factor loadings of a smaller magnitude were observed for the specific dimensions (Fig. 1)
We provide the first evidence that: (1) in patients, a positive correlation exists between the extent of premorbid cannabis use and the score on the positive symptom dimension, with daily users of high-potency cannabis showing the most positive symptoms at firstepisode psychosis (FEP); (2) psychotic experiences in nonclinical populations are associated with the current use of cannabis but are independent of the extent of lifetime exposure to cannabis; (3) negative symptoms at FEP are more common in patients who have never tried cannabis; (4) depressive symptoms are independent of any pattern of use of cannabis
Summary
There is compelling evidence to suggest that cannabis use is associated with psychotic disorders (Marconi, Di Forti, Lewis, Murray, & Vassos, 2016). Some reports suggest fewer negative symptoms in patients with psychosis who use cannabis (Bersani et al, 2002; Green et al, 2004; Peralta & Cuesta, 1992), which is consistent with having enough social skills to obtain the substance (Murray et al., 2017) This association has not been confirmed in other studies (Grech et al, 2005; Seddon et al, 2016) and others even reported a positive association (Ringen et al, 2016). Our findings provide the first large-scale evidence that FEP patients with a history of daily use of high-potency cannabis present with more positive and less negative symptoms, compared with those who never used cannabis or used lowpotency types
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