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07-12 Researchers find that cannabis may worsen psychotic symptoms

Researchers find that cannabis may worsen psychotic symptoms

A study led by Rashmi Patel, Ph.D., a researcher at King’s College London in the U.K., found that individuals who have recently experienced their first psychotic episode may endure worse treatment outcomes if they use cannabis within their first month of treatment.

The results of this study were published in the scientific journal BMJ Open.

The study

Scientists already know that individuals who use marijuana are at an increased risk of developing a psychotic episode, especially adolescents. Patel and colleagues, however, wanted to determine whether or not people with a history of psychosis are at a greater risk of experiencing another psychotic episode if they use cannabis.

The researchers analyzed health records of 2,026 people whose information was stored in the U.K.’s South London and Maudsley National Health Service Foundation Trust, one of the largest providers of mental health services in Europe. All participants had recently received treatment for psychosis.

To determine whether or not cannabis use influences psychotic symptoms, the researchers examined whether or not each patient used marijuana within a month of their first treatment visit. The researchers then tracked each patient’s treatment history — e.g., how frequently they were hospitalized, which medications they were prescribed and whether or not they were ever involuntarily committed to a hospital.

The results? Roughly half of the participants — or 46.3 percent — used cannabis within a month of initiating treatment for their first psychotic episode. Most participants who used cannabis during this time period were single men between the ages of 16 and 25.

Patients who used marijuana within the first month of treatment were 50 percent more likely to be readmitted to the hospital in the next five years than patients who abstained. Specifically, people who used cannabis early on in their treatment had an average of 1.8 hospital admissions over five years, whereas nonusers had an average of 1.2 admissions. On average, these hospital stays tended to be longer and became even longer over time — the average hospital stay for people who used cannabis increased from 21 days to 35 days in the three to five years after starting treatment.

People who used cannabis were also more likely to be involuntarily hospitalized within the first five years of treatment. Roughly half of all patients who used cannabis were involuntarily hospitalized (45 percent) compared to only a third of nonusers (34 percent).

Finally, the researchers found that individuals who use cannabis were more likely to be prescribed clozapine, a drug that is typically reserved for difficult-to-treat cases of schizophrenia. Patients who used cannabis were also more likely to be prescribed more drugs than nonusers, suggesting that their psychosis was more severe and/or more resistant to treatment.

What does this mean?

From this study, it seems as though using cannabis may worsen psychotic symptoms in people who have recently experienced their first psychotic episode. The researchers caution, however, that it’s difficult to draw firm conclusions about whether or not cannabis causes more severe symptoms, or whether or not people with more severe psychosis are more likely to use cannabis. More research is necessary before they can be certain.

“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,” wrote the researchers.

Sovereign Health of Rancho San Diego is a residential rehabilitation treatment provider that offers high-quality and comprehensive care for adolescents with mental illnesses, substance use disorders and co-occurring conditions. Patients at Sovereign Health receive a personalized treatment program that will help them overcome their addiction and/or deal with their mental health issues. Sovereign Health believes that by treating our patients as individuals — rather than using a one-size-fits-all method — we provide one of the best treatment plans in the country. For more information, contact our 24/7 helpline.

About the author

Courtney Lopresti, M.S., is a senior staff writer for Sovereign Health, where she uses her scientific background to write online blogs and articles for a general audience. At the University of Pittsburgh, where she earned her master’s in neuroscience, she used functional neuroimaging to study how the human cerebellum contributes to language processing. In her spare time, she writes fiction, reads Oliver Sacks and spends time with her two cats and bird. Courtney is currently located in Minneapolis. For more information and other inquiries about this article, contact the author at

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