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Impact of cannabis use on clinical outcomes and treatment failure in first episode psychosis

Research output: Contribution to journalMeeting abstract

Original languageEnglish
Article number16008
Pages (from-to)M111
Publication statusAccepted/In press - 4 Apr 2016


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Background: Cannabis is frequently used by people with first episode psychosis (FEP), though its effect on clinical outcome is less clear. We investigated whether cannabis use may be associated with increased risk of hospitalization and whether antipsychotic treatment failure, as indexed by number of unique antipsychotics prescribed, may mediate this effect in a large dataset of patients with FEP.

Methods: Data were obtained from electronic health records of 2,026 people with FEP in the South London and Maudsley NHS Foundation Trust (SLaM) using the Clinical Record Interactive Search tool (CRIS). Cannabis use was identified using natural language processing. Data on subsequent hospital admission and the number of unique antipsychotics prescribed (a marker of treatment failure) were obtained and analyzed using multivariable regression and mediation analyses with age, gender, ethnicity, marital status and diagnosis as covariates.

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 (odds ratio 1.55, 1.16 to 2.08) and greater number of inpatient days (B coefficient 35.1 days, 12.1 to 58.1). Antipsychotic treatment failure 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 (NIE: 1.27, 1.03 to 1.58; TE: 1.76, 0.81 to 3.84) and greater number of inpatient days (NIE: 17.9, 2.4 to 33.4; TE: 34.8, 11.6 to 58.1).

Discussion: Cannabis use in patients with FEP was associated with increased likelihood and duration of hospital admission. This was linked to the prescription of several different antipsychotic drugs, indicating clinical judgement of antipsychotic treatment failure. This suggests that cannabis use might be associated with worse clinical outcomes in psychosis by contributing towards failure of antipsychotic treatment.

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