Daily use of high-potency cannabis is associated with more positive symptoms in first-episode psychosis patients: the EU-GEI case-control study

Abstract

Background: 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.

Method: 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.

Results: 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.

Conclusions: 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.

Keywords: Cannabis use; cannabis-associated psychosis; first episode psychosis; psychopathology; psychotic experiences; symptom dimensions.

Fig. 1.

Bifactor model of psychotic experiences in controls. (□) Observed variables (No. of CAPE items); (○) Unobserved variables (latent factors); (→) standardized item loading estimation onto latent factors; G, general psychosis-like factor; Specific psychotic experiences factors: DEP, Depression; NEG, Negative; POS, Positive. Reliability and strength estimates: H = construct reliability index; ω = McDonald omega; ω_H = hierarchical omega; ω/ω_H = Relative omega. Explanatory note: McDonald‘s ω is an estimate of the proportion of the common variance accounted by general and specific symptom dimensions (Rodriguez et al., 2016). Relative omega (ω/ω_h) is the amount of reliable variance explained in the observed scores attributable to (a) the general factor independently from the specific symptom dimensions, and (b) each specific symptom dimension independently from the general factor. H is an index of the quality of the measurement model based on the set of CAPE items for each dimension (Hancock & Mueller, 2001). Indices can range from 0 to 1, with values closer to 1 indicating a better construct reliability and replicability across studies.

Fig. 2.

Positive symptom dimension in cases by patterns of cannabis use. Explanatory note: the positive symptom dimension predicted mean of each group of patterns of cannabis use is plotted against the predicted grand mean of all groups (represented by the red line). The positive value for the contrast of daily use of high-potency cannabis indicates more positive symptomatology in this group. On the other hand, negative values for the contrasts of the first two groups indicates less positive symptomatology when there is less exposure to cannabis. These differences are relevant, as indicated by 95% confidence intervals that do not overlap with zero. The model was a random intercept model which allowed symptoms to vary across countries and sites within countries, but it assumed that frequency of use and type of cannabis had an individual fixed effect. Values were adjusted for age, sex, ethnicity, diagnosis and use of other recreational/illicit substances.

Fig. 3.

Negative symptom dimension in cases by patterns of cannabis use. Explanatory note: the negative symptom dimension predicted mean of each group of patterns of cannabis use is plotted against the predicted grand mean of all groups (represented by the red line). Subjects who had never used cannabis presented with more negative symptoms compared to the whole sample. The model was a random intercept model which allowed symptoms to vary across countries and sites within countries, but it assumed that frequency of use and type of cannabis had an individual fixed effect.