A major new study shows that people who abuse the drug are more likely to be diagnosed with depression and bipolar disorder.
By Susan Pinker, Wall Street Journal | July 6, 2023
Psychologist Susan Pinker explores new discoveries in the science of human nature. Read previous columns here.
There was a new smell to New York City on my first visit since the pandemic. The New York I remember from 2018 was scented with subway fumes, car exhaust and pretzels. Now the air was a heady blend of forest fire, car exhaust and cannabis.
Recreational marijuana was legalized in the state of New York in 2021. But even if cannabis is easy and legal to buy in 23 states and all of Canada, the risks of chronic use aren’t talked about much.
People diagnosed with cannabis use disorder were almost twice as likely to be diagnosed later with clinical depression.
Several studies have shown that chronic cannabis use is linked to a higher incidence of schizophrenia among men in their early 20s, the age when the disease is usually diagnosed. The first paper on the topic, a Swedish study published in 1997, found that heavy cannabis use was associated with a sixfold increase in schizophrenia risk. In the decades since, social scientists have unearthed a strong link between heavy cannabis use and other severe psychological illnesses, including clinical depression and bipolar disorder.
Now a new longitudinal study has examined the medical records of all citizens of Denmark over the age of 16, some 6.5 million people in all, for patterns of diagnosis, hospitalization and treatment for substance use between 1995 and 2021. In the paper, published in the journal JAMA Psychiatry in May, Dr. Oskar Hougaard Jefsen of Aarhus University and colleagues showed that people who had previously been diagnosed with cannabis use disorder were almost twice as likely to be diagnosed later with clinical depression. According to the Centers for Disease Control and Prevention, cannabis use disorder is characterized by craving marijuana, using it more often than intended, spending a lot of time using it, and having it interfere with friends, family and work.