Heavy marijuana use increases schizophrenia in men, study finds

Young men who use potent marijuana frequently have an increased risk of developing schizophrenia, according to a new study of nearly 7 million health records.

According to study published Thursday in Psychological Medicine. According to previous research, the condition, loosely defined as frequent drug use despite negative consequences, develops in about three out of 10 people who use marijuana. The latest study, based on Danish health records, adds to the growing research on cannabis and mental health outcomes in the United States and other countries.

“The tangle of substance use disorders and mental illness is a major public health issue, requiring urgent action and support for those who need it,” said co-author Nora Volkow, who is also director of the Danish National Institute for Drug Addiction.

While the Danish population isn’t as diverse as the United States, and genetics plays a role in schizophrenia risk, the results should apply to people of all ethnic backgrounds, Volkow said in an interview.

“The evidence is strong enough to encourage caution,” Volkow said, especially for people with a family history of schizophrenia or early symptoms of the mental disorder.

Schizophrenia, characterized by loss of contact with reality and symptoms such as delusions and hearing voices, can be a lifelong illness that is difficult to treat. The economic burden of schizophrenia in the United States was $343.2 billion in 2019, more than double what it was in 2013, according to a study by the Clinical Journey of Psychiatry.

The new study is the first to show the relationship between cannabis use disorder and schizophrenia in a large population. Previous research has shown links between the use of cannabis with high levels of its psychoactive compound THC and psychosis, the loss of contact with reality that is a main symptom of schizophrenia. Cannabis use at an earlier age and more frequent use are also thought to increase the risk.

Although cannabis use disorder is not responsible for most cases of schizophrenia in Denmark, the study found that it has contributed to a growing number over the past five decades. There was a significant difference between women and men; in the 16-49 age group, the study estimated that 15% of schizophrenia cases in men could be prevented if they avoided cannabis use disorders, but only 4% of cases would be affected in women.

The finding comes as many US cannabis companies say they are increasing the potency of their products to meet consumer demand. Some US states and Germany have recently considered limiting the potency of marijuana.

Cannabis is widely perceived as non-addictive and considered beneficial for certain mental health conditions. But recent studies have shown that cannabis addiction rates among teens are about the same as for prescription opioids, that there are serious risks from second-hand smoke, using the drug during pregnancy and an increased risk of heart disease. Some companies see opportunities to treat cannabis use disorders.

The authors said the growing number of schizophrenia cases that can be traced to cannabis use disorder, which has increased over the past 50 years, is likely due to the increasing potency of cannabis, as well as a diagnosis disease more common.

Carsten Hjorthøj, lead author of the study, said legalization has led to a change in attitude, as fewer people perceive the drug as dangerous. “This study adds to our growing understanding that cannabis use is not safe,” Hjorthøj said in a statement.

More stories like this are available at bloomberg.com

©2023 Bloomberg LP