Cases of Schizophrenia Associated with Marijuana Use See an Increase


Cases of schizophrenia linked to cannabis use disorder have increased 3- to 4- fold in the past 25 years.

According to the World Health Organization (WHO), approximately 20 million people worldwide suffer from schizophrenia. The chronic mental disorder is characterized by delusions, hallucinations, and psychosis. Despite no cure, current therapeutic interventions are quite effective at managing the symptoms. The exact cause of schizophrenia is still unclear; however, researchers believe a combination of genetic and environmental factors are to blame. Although there is no confirmed link between cannabis use and schizophrenia, previous studies have suggested that heavy and frequent use may predispose people to a mental disorder.

Cannabis use is often a controversial topic around the globe due to its various effects. The drug has shown many medical benefits, such as treating migraines and reducing seizures in childhood epilepsy. Furthermore, several countries have legalized the drug for both medicinal and recreational uses. However, researchers believe legalization can cause cannabis use disorder among the masses. And result in psychiatric concerns, increased road traffic accidents, unemployment, and other social problems. Over the years, several countries including Denmark have reported a drastic increase in the use of cannabis. Now, researchers want to see whether this rise is accompanied by an increase in cases of schizophrenia.

A team of researchers in Denmark conducted a nationwide study, analyzing the medical records of more than 7 million people. They aimed to assess the change in cases of cannabis use disorder and schizophrenia from 1972 to 2016. The study included all those born before December 31, 2000; ensuring the participants were alive or at least 16-years old during follow up. They published their findings in the journal JAMA Psychiatry.

Is There a Link?

According to the results, around 2% of Denmark’s schizophrenia cases in 1995 were associated with cannabis addiction. This rose to 4% in 2000 and since 2010 the figure has stood at 8%. Thus, revealing a 3- to 4- fold increase in cases.

Although the findings are not actual proof of a link between the two, study authors believe the results are highly suggestive of the harmful effects of cannabis use disorder. Moreover, they believe that their study establishes cannabis as a ‘component cause’ of schizophrenia. 

The proportion of cases of schizophrenia associated with cannabis use disorder has increased 3- to 4-fold during the past 2 decades, which is expected given previously described increases in the use and potency of cannabis.

study authors

As more and more countries move to legalize the use of cannabis, study authors believe this can likely increase its perception as a harmless drug among people. Therefore, they call for a reduction in the potency of the drug available on the market and for better legalization laws.

I think it is highly important to use both our study and other studies to highlight and emphasize that cannabis use is not harmless

Professor Carsten Hjorthøj, study author


Hjorthøj C, Posselt CM, Nordentoft M. Development Over Time of the Population-Attributable Risk Fraction for Cannabis Use Disorder in Schizophrenia in Denmark. JAMA Psychiatry. Published online July 21, 2021. doi:10.1001/jamapsychiatry.2021.1471


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