Researchers found that first-episode psychosis patients who used cannabis were much more likely to be readmitted to the hospital after initial treatment.
Psychosis is a term used to describe symptoms of a mental illness that cause a person to lose touch with reality, such as hallucinations or delusions. These are often symptoms of disorders such as schizophrenia, bipolar or post-traumatic stress disorder (PTSD).
According to the National Alliance on Mental Illness (NAMI), around 3 in 100 people in the US will experience a psychotic episode at some point in their lives, with young adults most at risk.
Previous research has suggested that individuals who use cannabis are at greater risk of psychotic episodes, particularly if they use the drug in adolescence.
However, study coauthor Dr. Rashmi Patel, of the Department of Psychosis Studies at King's College London in the UK, and colleagues note that it is unclear whether people who are already experiencing a psychotic episode are at greater risk for relapse as a result of cannabis use.
With a view to finding out, the team analyzed the health records of 2,026 people who had been treated for a first episode of psychosis at the UK's South London and Maudsley (SLaM) National Health Service (NHS) Foundation Trust between 2006-2013.
The researchers assessed patients' cannabis use within a month of their first treatment visit and tracked any subsequent treatment and outcomes for the following 5 years.
More hospital admissions, antipsychotic prescriptions for cannabis users
The health records revealed that around 46.3% of the patients were using cannabis within 1 month of initiating treatment for a first psychotic episode, with use of the drug most common among single men aged 16-25.
Compared with patients who did not use cannabis, those who did were 50% more likely to be readmitted to the hospital in the 5 years after initial treatment; cannabis users had an average of 1.8 hospital admissions over the 5 years, while non-users had an average of 1.2 admissions.
Cannabis users were also more likely to experience compulsory hospital detention under the UK's Mental Health Act, with 45% of users being sectioned, compared with 34% of those who did not use the drug.
Psychosis patients who used cannabis were also at greater risk for longer hospital stays, particularly after completion of 2 years of treatment; compared with non-users, the average hospital stay for those who used cannabis increased from 21 days to 35 days in the 3-5 years after starting treatment.
What is more, the researchers found that cannabis users were more likely to be prescribed a drug called clozapine - commonly used for hard-to-treat schizophrenia - and had a higher number of prescriptions for a range of other antipsychotic medications in the 5 years after first treatment, compared with non-users.
Cannabis use may lead to antipsychotic treatment failure
The authors say they were unable to gather enough information from the health records to determine whether the greater number of antipsychotic prescriptions among cannabis users was driven by poor treatment response, poor compliance or other factors.
Still, they note that prescription of a variety of different antipsychotic drugs is a strong indicator of treatment failure.
Overall, they believe the findings suggest that cannabis use might be linked to worse clinical outcomes for patients with psychosis, partly mediated by the failure of antipsychotic treatment.
Commenting on the results, the authors say:
"Taken together, these findings highlight the importance of ascertaining cannabis use in people receiving care for psychotic disorders and prompt further study to investigate the mechanisms underlying poor clinical outcomes in people who use cannabis and strategies to reduce associated harms."
Medical News Today recently reported on a study linking cannabis use to impaired processing of emotions.