A new study has found that young men with cannabis (marijuana) use disorder, or CUD, could have an increased risk of developing schizophrenia.
The research, published on May 4 in the journal Psychological Medicine, examined the health records of 6.9 million people in Denmark aged 16 to 49 from 1972 to 2021. The Centers for Disease Control and Prevention (CDC) defines CUD as the inability to stop using marijuana despite negative impacts on one’s health and social life.
Researchers found an association between CUD and schizophrenia among men and women, but the association was much stronger in men because fewer women are subject to CUD than men.
Up to 30 percent of cases of schizophrenia among men between 21 and 30 years old could have been prevented by avoiding cannabis use disorder, according to the study.
The findings also estimated that 15 percent of schizophrenia cases occurring in men ages 16 to 49 could be averted if they avoided CUD, while only 4 percent of cases affecting women in the same age range.
“Although CUD is not responsible for most schizophrenia cases in Denmark, it appears to contribute to a non-negligible and steadily increasing proportion over the past five decades,” the researchers said.
The researchers noted previous studies linking schizophrenia and CUD and wanted to focus on how the relationship is impacted by age and gender.
Some studies suggest the possible cause of this link is due to heavy use or the increase in cannabis potency, measured by the percentage of delta-9-tetrahydrocannabinol (THC). According to the report, THC levels increased from 13 percent in 2006 to 30 percent in 2016 in Denmark. THC potency in cannabis products was typically less than 2 percent prior to the 1980s, but current potency in commonly used oils and edibles reaches upwards of 95 percent.
Twenty-one U.S. states and the District of Columbia have legalized cannabis for recreational use for people aged 21 and up, while 39 states plus the District of Columbia have legalized it for medical use.
“Increases in the legalization of cannabis over the past few decades have made it one of the most frequently used psychoactive substances in the world, while also decreasing the public’s perception of its harm. This study adds to our growing understanding that cannabis use is not harmless, and that risks are not fixed at one point in time,” Carsten Hjorthøj, lead author of the study and associate professor at the Mental Health Services in the Capital Region of Denmark and at the University of Copenhagen, said in a press release.
In 2020, there were more than 3.4 million recreational cannabis users in the United States. This number is expected to double in 2025. According to the CDC, an estimated three in 10 marijuana users have CUD. Furthermore, the country is now home to an estimated 3.6 million state-legal medical cannabis patients. Last year, the U.S. cannabis market size was valued at $13.2 billion; by 2025, it’s expected to be worth more than $45 billion.
Schizophrenia is a chronic, severe, and disabling mental disorder. Its symptoms can include delusions, disordered thoughts, and hallucinations.
People with schizophrenia often have difficulty differentiating between physical and imaginary experiences, thinking logically, expressing normal emotions, or behaving normally.
Worldwide, schizophrenia affects 20 million people. No cure exists, so doctors try to manage the symptoms with medications and therapy.
In the United States, the National Institute of Mental Health said it’s hard to obtain accurate estimates of the prevalence of schizophrenia because diagnosis is complex and it overlaps with other disorders.
CNN Wire, Hilary A. Marusak, and John Mac Ghlionn contributed to this report.