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UBC Theses and Dissertations

Factors associated with the onset of schizophrenia and long term psychosis in adolescents who consume cannabis : a systematic review of the evidence Wagner, Brandy


During adolescence the brain undergoes critical neurodevelopment. It is a time when some teens are at increased risk for developing early onset schizophrenia, and when recreational cannabis use is high. Over the past 25 years, a growing body of schizophrenia research has focused on examining linkages between heavy (daily, or >50 times in a lifetime) cannabis use during adolescence and early onset of the disorder during adolescence. Findings suggest an association between neurodevelopment, heavy cannabis use during adolescence and the development of early onset schizophrenia. To date no systematic review (SR) has provided a summary of the main findings or synthesis of the range of factors or has critiqued methodological quality of existing studies. The purpose of my thesis was to provide a synthesis which critically appraises the reporting and methodological quality of observational studies examining factors reported to be associated with early onset schizophrenia in adolescents (aged 10 to 19 years) with a history of heavy cannabis consumption. Nine electronic health databases (Google Scholar, the Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Reviews, the Database of Abstracts of Reviews of Effects (DARE), PubMed, MEDLINE, EMBASE, CINAHL, and PsycINFO) were systematically searched to locate relevant studies using predetermined eligibility criteria. Intra-rater reliability was used to reduce selection bias. Data from 16 eligible studies were synthesized using the Gerard method and the STROBE tool was used to appraise reporting and methodological quality of studies. The results of this SR show a strong positive association between heavy and frequent cannabis use during adolescence and early development of schizophrenia/psychotic symptoms. Findings also indicate that age at which cannabis is first used, genetic predisposition, and childhood trauma also increase this risk. The methodological quality of these 16 studies was generally strong however reporting on the handling of missing data, the inclusion of both male and female subjects, and power analyses would have strengthened the evidence. Findings of this SR have implications for nurses in areas of education, research and practice. There are also implications for policies amongst policy makers, and knowledge translation amongst youth, their families, and the general public.

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