title: Association of cannabis use with hospital admission and antipsychotic treatment failure in first episode psychosis: an observational study.
abstract: OBJECTIVE
  To investigate whether cannabis use is associated with increased risk of relapse, as indexed by number of hospital admissions, and whether antipsychotic treatment failure, as indexed by number of unique antipsychotics prescribed, may mediate this effect in a large data set of patients with first episode psychosis (FEP).
  
  
  METHODS
  Observational study with exploratory mediation analysis.
  
  
  METHODS
  Anonymised electronic mental health record data from the South London and Maudsley NHS Foundation Trust.
  
  
  METHODS
  2026 people presenting to early intervention services with FEP.
  
  
  METHODS
  Cannabis use at presentation, identified using natural language processing.
  
  
  METHODS
  admission to psychiatric hospital and clozapine prescription up to 5 years following presentation.
  Number of unique antipsychotics prescribed.
  
  
  RESULTS
  Cannabis use was present in 46.3% of the sample at first presentation and was particularly common in patients who were 16-25, male and single. It was associated with increased frequency of hospital admission (incidence rate ratio 1.50, 95% CI 1.25 to 1.80), increased likelihood of compulsory admission (OR 1.55, 1.16 to 2.08) and greater number of days spent in hospital (β coefficient 35.1 days, 12.1 to 58.1). The number of unique antipsychotics prescribed, mediated increased frequency of hospital admission (natural indirect effect 1.09, 95% CI 1.01 to 1.18; total effect 1.50, 1.21 to 1.87), increased likelihood of compulsory admission (natural indirect effect (NIE) 1.27, 1.03 to 1.58; total effect (TE) 1.76, 0.81 to 3.84) and greater number of days spent in hospital (NIE 17.9, 2.4 to 33.4; TE 34.8, 11.6 to 58.1).
  
  
  CONCLUSIONS
  Cannabis use in patients with FEP was associated with an increased likelihood of hospital admission. This was linked to the prescription of several different antipsychotic drugs, indicating clinical judgement of antipsychotic treatment failure. Together, this suggests that cannabis use might be associated with worse clinical outcomes in psychosis by contributing towards failure of antipsychotic treatment.
authors.affiliation: Department of Psychosis Studies, King's College London, Institute of Psychiatry, Psychology & Neuroscience, London, UK.
authors.forename: Rashmi
authors.identifier: http://orcid.org/0000-0002-9259-8788
authors.initials: R
authors.lastname: Patel
authors.affiliation: Department of Psychosis Studies, King's College London, Institute of Psychiatry, Psychology & Neuroscience, London, UK.
authors.forename: Robin
authors.initials: R
authors.lastname: Wilson
authors.affiliation: Department of Psychological Medicine, King's College London, Institute of Psychiatry, Psychology & Neuroscience, London, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Jackson
authors.affiliation: Department of Psychological Medicine, King's College London, Institute of Psychiatry, Psychology & Neuroscience, London, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Ball
authors.affiliation: South London and Maudsley NHS Foundation Trust, Biomedical Research Centre Nucleus, London, UK.
authors.forename: Hitesh
authors.initials: H
authors.lastname: Shetty
authors.affiliation: South London and Maudsley NHS Foundation Trust, Biomedical Research Centre Nucleus, London, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Broadbent
authors.affiliation: Department of Psychological Medicine, King's College London, Institute of Psychiatry, Psychology & Neuroscience, London, UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Stewart
authors.affiliation: Department of Psychosis Studies, King's College London, Institute of Psychiatry, Psychology & Neuroscience, London, UK.
authors.forename: Philip
authors.initials: P
authors.lastname: McGuire
authors.affiliation: Department of Psychosis Studies, King's College London, Institute of Psychiatry, Psychology & Neuroscience, London, UK.
authors.forename: Sagnik
authors.initials: S
authors.lastname: Bhattacharyya
mesh_terms: D000293:Adolescent; D000328:Adult; D014150:Antipsychotic Agents / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008131:London; D008297:Male; D008385:Marijuana Smoking / Q000453:epidemiology*; D015999:Multivariate Analysis; D010343:Patient Admission / Q000706:statistics & numerical data*; D011618:Psychotic Disorders / Q000188:drug therapy*; D012042:Registries; D017211:Treatment Failure; D055815:Young Adult
chemical_list: D014150:Antipsychotic Agents
keywords: CRIS; Cannabis; FEP; Mediation analysis; NLP; Natural Language Processing