Abstract
Although cannabis use after a first episode of psychosis has been associated with relapse, little is known about the determinants of this most preventable risk factor for relapse of psychosis. Here we aimed to study whether the effects on outcome vary depending on the type of cannabis consumed and usage pattern. In this observational study, we prospectively recruited and followed up patients aged 18-65 years who presented with their first episode of psychosis to psychiatric services in south London, London, UK. Relapse of psychosis within 2 years after onset of psychosis was defined as risk of subsequent admission to hospital. We classified patients into different patterns of cannabis use based on continuity of use after onset of psychosis, potency of cannabis consumed, and frequency of use after the onset of their illness. We used multiple regression analyses (logistic or binominal) to compare the different cannabis use groups and propensity score analysis to validate the results. Between April 12, 2002, and July 26, 2013, 256 patients presented with a first episode of psychosis. We did follow-up assessments for these patients until September, 2015. Simple analyses showed that former regular users of cannabis who stopped after the onset of psychosis had the most favourable illness course with regards to relapse. In multiple analysis, continued high-frequency users (ie, daily use in all 24 months) of high-potency (skunk-like) cannabis had the worst outcome, indexed as an increased risk for a subsequent relapse (odds ratio [OR] 3·28; 95% CI 1·22-9·18), more relapses (incidence rate ratio 1·77; 95% CI 0·96-3·25), fewer months until a relapse occurred (b -0·22; 95% CI -0·40 to -0·04), and more intense psychiatric care (OR 3·16; 95% CI 1·26-8·09) after the onset of psychosis. Adverse effects associated with continued use of cannabis after the onset of a first episode of psychosis depend on the specific patterns of use. Possible interventions could focus on persuading cannabis-using patients with psychosis to reduce use or shift to less potent forms of cannabis. National Institute for Health Research (NIHR).
Highlights
In the past 30 years, findings of studies have shown that cannabis use is a contributory cause of psychotic disorders, especially if used often and initiated at an early age.[1,2] Cannabis remains the most commonly used illicit drug in patients with established psychosis[3] and use is especially high in young people presenting with their first episode of psychosis.[4]
Evidence before this study In January, 2016, we published a meta-analysis in The Lancet Psychiatry, wherein we studied the effect of continued cannabis use on the risk of relapse in patients with psychosis
Referral to community team only Required contact with crisis team Required hospital admission Required hospital admission Months stayed in hospital at onset Employment status at onset (n in employment)† Family history of mental illness Onset diagnosis Medication prescribed at onset Type of medication at onset Second-generation antipsychotic First-generation antipsychotic
Summary
In the past 30 years, findings of studies have shown that cannabis use is a contributory cause of psychotic disorders, especially if used often and initiated at an early age.[1,2] Cannabis remains the most commonly used illicit drug in patients with established psychosis[3] and use is especially high in young people presenting with their first episode of psychosis.[4]. How parameters of cannabis use, such as type and potency of cannabis used and frequency of use, affect outcome has remained unclear This gap in the scientific literature is especially important in view of findings that dose, type, and pattern[10] of cannabis use are important determinants of its effect on onset of psychosis. For such evidence to be translated into real world meaningful solutions in the clinical setting, it is important to develop a more nuanced understanding of the association between one of the most potentially www.thelancet.com/psychiatry Vol 3 October 2016
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