People with psychosis who take cannabis have a 50% increased chance of being hospitalised, researchers warned today.
The largest observational study of its kind, from King’s College, London, also reveals that cannabis use is linked to higher numbers of prescriptions for different antipsychotic drugs.
Although cannabis use has been linked to an increased risk of psychotic episodes, particularly among teenagers, researchers set out to establish if it has an impact on relapse risk in those with long term psychosis.
They examined anonymised electronic health records of 2026 people who treated for a first episode of psychosis at one of the largest providers of mental health services in Europe between 2006 and 2013.
Cannabis use was recorded in the records of 46.3% of those using early intervention services within a month of the start of treatment. Use was particularly prevalent among single men, aged between 16 and 25.
Writing in BMJ Open, they say that cannabis consumption was associated with a 50% increase in hospital admission frequency, with an average of 1.8 admissions up to five years after the first service visit. This compared with an average of 1.2 admissions among non-users over the same period.
Users of the drug were also 45% more at risk of compulsory detention in hospital under the Mental Health Act, compared with 34% of non users, while cannabis consumers were more likely to stay in hospital for longer, increasing from an average of 21 extra days within three years, to 35 additional days within five years.
The researchers also found that cannabis users were more likely to be treated with clozapine, an antipsychotic used for difficult-to-treat schizophrenia, and up to 11 prescriptions for different antipsychotics.
Although the researchers were unable to ascertain if number of different prescriptions was prompted by poor treatment response, poor compliance, unpleasant side effects, or admission to hospital following a relapse, they suggest that antipsychotic prescriptions are indicative of treatment failure.
This points to a link between cannabis use and increased risk of hospital admission linked to treatment failure.
Researcher Dr Rashmi Patel said last night: "The findings of this study are important as they highlight a need for clinicians to help address cannabis use among people with psychotic disorders."
He added: "Our study highlights a clear link between cannabis use and poor clinical outcomes in people with established psychotic disorders.
"However, further research is needed to determine the exact mechanisms by which cannabis use results in poorer outcomes, as well as to develop better treatment strategies for people with psychotic disorders who use cannabis."
Patel R, Wilson R, Jackson R et al. Association of cannabis use with hospital admission and antipsychotic treatment failure in first episode psychosis: an observational study. BMJ Open. 4 March 2016; doi 10.1136/bmjopen-2015-009888 [abstract]
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