Psychotic-like Experiences and Age at First Use of Cannabis in a Non-clinical Sample

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Barnes, Erica R.
thesis / dissertation description
Previous research has demonstrated a relationship between cannabis use and several aspects of psychosis (development, decreased age of onset, exacerbation of symptoms and increased relapse). Unanswered questions concern whether there are ages of vulnerability for cannabis exposure. Further, despite gender differences in the development, age of onset, severity and overall course of psychosis, no research has examined the effect of cannabis exposure and psychotic-like experiences (PLE) across gender. The current study examined 428 undergraduate University students divided into three groups: cannabis use before age 16 (prepuberty group), cannabis use after age 16 (postpuberty group), and a control group. Lifetime cannabis use was divided into low (1-9 times) and high (10 or more times) amounts. It was predicted that males in the prepuberty group with high lifetime cannabis use would have the highest PLE as measured by the Perceptual Aberration and Magical Ideation (Per-Mag) scales from the Chapman Psychosis Proneness Scale, the Community Assessment of Psychic Experiences (CAPE) positive symptoms scale and the CAPE positive symptoms distress scale. Loglinear analyses revealed, contrary to the hypothesis, that females experienced higher PLE in the prepuberty group and males had higher PLE in the postpuberty group, as measured by the Per-Mag scale. The CAPE positive symptoms and distress scales failed to reveal any significant findings. Also, lifetime cannabis use was not found to significantly contribute to this model. These findings support and expand previous research that there are indeed periods of vulnerability for cannabis exposure and subsequent effects on PLE. Gender was found to mediate this effect where males and females have opposite periods of vulnerability.