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Greater Marijuana Use Linked to More Severe Schizophrenia

Greater Marijuana Use Linked to More Severe SchizophreniaNew research reveals that schizophrenia patients with a history of cannabis use have longer hospital stays and a higher rate of hospital readmission.

They may also have a type of schizophrenia “that may be more severe than schizophrenia cases in general,” according to Peter Allebeck, M.D., Ph.D., professor of social medicine in the Department of Public Health Sciences at the Karolinska Institute in Stockholm, Sweden.

For the study, 50,087 male Swedish army recruits (ages 18 to 19 years) underwent medical assessments as well as structured interviews by psychologists, including questions on family and socioeconomic background, work, leisure activities, and use of alcohol, drugs, and tobacco.

At baseline, there were no statistically significant differences between cannabis users and nonusers in terms of psychiatric diagnoses.

Of the 50,087 participants, 5391 used cannabis. During follow-up, 350 patients were identified as having schizophrenia, and of these, 58 used cannabis.

At first admission for schizophrenia, the only schizophrenia subtype showing a difference was paranoid schizophrenia, for which cannabis users had a lower rate compared with nonusers.

The length of stay during the first hospital admission was almost twice as long for users as for nonusers (59 days vs 30 days). One third of users (34 percent) required more than 90 days, whereas only 20 percent of nonusers were hospitalized that long on first admission.

Similarly, cannabis users had a median of 10 readmissions compared to 4 readmissions for nonusers. Nearly a third of the cannabis users had more than 20 readmissions — 29 percent of users vs 10 percent of nonusers.

“Those who had schizophrenia after cannabis use had many more hospital days…more than a third [38 percent] of those who had cannabis use had more than 2 years in total in hospital stay” compared with 21 percent of nonusers, said Allebeck. The median number of hospital days was 547 for cannabis users and 184 for nonusers.

After controlling for socioeconomic factors, personality disorders, IQ, and other factors associated with cannabis use, “there was more than three-fold increased risk of such long hospital days among cannabis users,” said Allebeck.

“The number of readmissions is also about three-fold increased of those with many readmissions after the first admission for schizophrenia,” he said.

“Schizophrenia caused by or contributed by cannabis may be more severe than schizophrenia in general,” he concluded.

“Patients with cannabis history seem to have more severe and more persistent history of schizophrenia, as indicated by duration of first admission, total duration of hospital days, number of readmissions. And these of course are true measures of severity and prognosis.”

The findings were reported at EPA 2013: 21st European Congress of Psychiatry.

Source:  21st European Congress of Psychiatry

Greater Marijuana Use Linked to More Severe Schizophrenia

Traci Pedersen

Traci Pedersen is a professional writer with over a decade of experience. Her work consists of writing for both print and online publishers in a variety of genres including science chapter books, college and career articles, and elementary school curriculum.

APA Reference
Pedersen, T. (2018). Greater Marijuana Use Linked to More Severe Schizophrenia. Psych Central. Retrieved on November 28, 2020, from
Scientifically Reviewed
Last updated: 8 Aug 2018 (Originally: 13 Apr 2013)
Last reviewed: By a member of our scientific advisory board on 8 Aug 2018
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