U-shaped curve of psychosis according to cannabis use: New evidence from a snowball sample

Abstract

Background: The aim of this study was to investigate the relationship between psychotic-like experiences (PLEs) assessed using the Community Assessment of Psychic Experience (CAPE) questionnaire and the pattern of cannabis use in a non-clinical sample collected by snowball sampling. Methods: Our sample was composed of 204 subjects, distributed into three groups by their cannabis use pattern: 68 were non-cannabis users, 40 were moderate cannabis users and 96 were daily cannabis users. We assessed the psychotic experiences in each group with the CAPE questionnaire; and then controlled for the effect of possible confounding factors like sex, age, social exclusion, age of onset of cannabis use, alcohol use and other drug use. Results: We found a significant quadratic association between the frequency of cannabis use and positive (β = −1.8; p = 0.004) and negative dimension scores (β = −1.2; p = 0.04). The first-rank and mania factors showed a significant quadratic association ( p < 0.05), while the voices factor showed a trend ( p = 0.07). Scores for the different groups tended to maintain a U-shape in their values for the different factors. When we adjusted for gender, age, social exclusion, age of onset of cannabis use, and use of alcohol and other drugs, only the first-rank experiences remained significant. Conclusions: We found there was a U-shaped curve in the association between cannabis use and the positive and negative dimensions of the CAPE score. We also found this association in mania and first-rank experiences.