Cannabis use and symptom severity in individuals at ultra high risk for psychosis: a meta-analysis.
We aimed to assess whether individuals at ultra high risk (UHR) for psychosis have higher rates of cannabis use and cannabis use disorders (CUDs) than non-UHR individuals and determine whether UHR cannabis users have more severe psychotic experiences than non-users.



We conducted a meta-analysis of studies reporting cannabis use in the UHR group and/or positive or negative symptoms among UHR cannabis users and non-users. Logit event rates were calculated for cannabis use, in addition to odds ratios to assess the difference between UHR and controls. Severity of clinical symptoms in UHR cannabis users and non-users was compared using Hedges' g.



Thirty unique studies were included (UHR n = 4205, controls n = 667) containing data from cross-sectional and longitudinal studies, and randomised control trials. UHR individuals have high rates of current (26.7%) and lifetime (52.8%) cannabis use, and CUDs (12.8%). Lifetime use and CUDs were significantly higher than controls (lifetime OR: 2.09; CUD OR: 5.49). UHR cannabis users had higher rates of unusual thought content and suspiciousness than non-users.



Ultra high risk individuals have high rates of cannabis use and CUDs, and cannabis users had more severe positive symptoms. Targeting substance use during the UHR phase may have significant benefits to an individual's long-term outcome.
Division of Psychology and Mental Health, University of Manchester, Manchester, UK.
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0000-0002-2859-6825
R
Carney
Division of Psychology and Mental Health, University of Manchester, Manchester, UK.
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0000-0002-3414-6265
J
Cotter
Division of Psychology and Mental Health, University of Manchester, Manchester, UK.
J
J
Firth
Division of Nursing, Midwifery and Social Work, University of Manchester, Manchester, UK.
T
T
Bradshaw
Division of Psychology and Mental Health, University of Manchester, Manchester, UK.|Greater Manchester West Mental Health NHS Foundation Trust, Manchester, UK.
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AR
Yung
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000453:epidemiology*; D000074609:Marijuana Use / Q000453:epidemiology*; D011618:Psychotic Disorders / Q000453:epidemiology* / Q000503:physiopathology*; D012306:Risk; D012720:Severity of Illness Index
at-risk mental state; cannabis; clinical high risk; prodrome; substance use; ultra high risk