Cannabis in First-Episode Psychosis Linked to Poor Outcomes

Megan Brooks

March 08, 2016

Cannabis use by patients with first-episode psychosis (FEP) is associated with significantly worse clinical outcomes over time, a large, retrospective study shows.

Investigators from King's College London, in the United Kingdom, found that cannabis users were 50% more likely to be admitted to hospital in the 5 years after initial FEP treatment and that length of stays in hospital were longer for these patients.

"We also found that the poor outcomes associated with cannabis use may be linked to antipsychotic treatment failure," study investigator Rashmi Patel, BMBCh, told Medscape Medical News.

"The findings of this study are important, as they highlight a need for greater emphasis to reduce the risks of cannabis use among people with FEP and to determine how to optimize treatment in this group of patients," Dr Patel said.

The study was published online March 3 in BMJ Open.

Contributor to Treatment Failure?

Previous research has suggested that cannabis use is associated with an increased risk of developing a psychotic disorder, but until now, little was known about the effects of cannabis on individuals with an established psychotic disorder, said Dr Patel.

The researchers analyzed deidentified electronic health records for 2026 adults treated for FEP at a large mental health care service provider in Europe between 2006 and 2013. Patients were followed for up to 5 years.

At presentation for FEP, cannabis use was noted in the records of 939 individuals (46.3%), consistent with the high levels of lifetime cannabis use seen in other FEP studies, the authors note. In this sample, cannabis use was particularly common in young, single men.

Cannabis use was associated with increased frequency of hospital admission (incidence rate ratio, 1.50; 95% confidence interval [CI], 1.25 - 1.80) and increased odds of a compulsory admission (odds ratio, 1.55; 95% CI, 1.16 - 2.08).

Cannabis use was also associated with a greater number of days spent in the hospital. During follow-up, length of stay progressively increased for cannabis users, from an average of 21 extra days within 3 years to 35 additional days within 5 years.

Dr Rashmi Patel

The records also showed that at initial presentation for FEP, cannabis users were more apt to be treated with clozapine (multiple brands), an antipsychotic used for difficult-to-treat schizophrenia, and to receive a higher number of individual antipsychotics (up to 11), which is a proxy marker for treatment failure, the investigators note.

To their knowledge, this is the first published study to "demonstrate the potential mediation of cannabis use with poorer outcomes by a failure of antipsychotic treatment," they write.

Owing to the observational nature of the study, no firm conclusions can be drawn about cause and effect, they point out. However, they say their findings "highlight the importance of ascertaining cannabis use in people receiving care for psychotic disorders." The findings should also "prompt further study to investigate the mechanisms underlying poor clinical outcomes in people who use cannabis and strategies to reduce associated harms."

Teasing Out Confounders

Commenting on the findings for Medscape Medical News, Subroto Ghose, MD, PhD, University of Texas Southwestern Medical Center, in Dallas, said the study is interesting and demonstrates associations between initial cannabis use and poorer outcomes.

"There are, however, certain potential confounders that need to be teased out. The major ones are whether the subjects continued to use cannabis after the index admission. Are there differences between those who stopped using compared to those who continue to use cannabis? Many subjects who use cannabis also use other illicit drugs. How did other substance use impact the results of the study?" he asked.

Dr Ghose also noted that although the greater number of medications prescribed to cannabis users "could reflect nonresponsiveness, there are several other reasons why a person could have been prescribed different medications. These include medication tolerability, side effects (as mentioned by the authors), and compliance. These data suggest the need for carefully designed prospective studies in this population," Dr Ghose concluded.

The study received no specific funding. Several investigators have received funding from pharmaceutical companies, which are listed in the original article.

BMJ Open. Published online March 3, 2016. Full text

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