Abstract
ObjectiveWe 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.MethodWe 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.ResultsThirty 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.ConclusionUltra 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.
Highlights
IntroductionPeople with schizophrenia are more likely to use cannabis and have comorbid substance use disorders than the general population [8]
Cannabis is one of the most frequently used illicit drugs worldwide [1]
Proportionate meta-analysis revealed that 26.7% of ultra high risk (UHR) individuals currently used cannabis (n = 3068, 95% CI = 0.22–0.32; I2: 85.70%; Fig. 2)
Summary
People with schizophrenia are more likely to use cannabis and have comorbid substance use disorders than the general population [8]. This increased comorbidity is associated with poor clinical outcomes: increased premature mortality, poor engagement with services and increased rates of hospitalisation [9, 10]. High rates of cannabis use are often observed at an early stage, in people with first-episode psychosis (FEP; [11]). This unhealthy profile may even predate the onset of full psychotic symptoms, during the ultra high risk (UHR) phase
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