NIDA Study Finds Young Men At Higher Risk Of Schizophrenia Linked With Cannabis Use Disorder

Young men with cannabis use disorder, or excessive dependency on marijuana consumption, are at higher risk of developing schizophrenia, according to a study led by researchers at the Mental Health Services in the Capital Region of Denmark and the National Institute on Drug Abuse (NIDA) at the National Institutes of Health. 

The study, published in Psychological Medicine, analyzed health records spanning five decades and representing more than 6 million people in Denmark to estimate the fraction of schizophrenia cases that could be attributed to cannabis use disorder on the population level.

What Is Cannabis Use Disorder?

While there does not appear to be any evidence that users develop physiological dependencies for cannabis in the same way that they do for cocaine or opioids, cannabis dependence affects a small subsection of the population. While NIDA cites delusions and psychosis as side effects of smoking high-potency cannabis on a regular basis, it does not mention common scientific evidence that any stressor can serve as a trigger to a psychotic episode.

That said, the Denmark/NIDA study notes that cannabis use disorder and schizophrenia can both be treated. 

Researchers found strong evidence of an association between cannabis use disorder and schizophrenia among men and women, though the association was much stronger among young men. Using statistical models, the study authors estimated that as many as 30% of cases of schizophrenia among men aged 21-30 might have been prevented by averting cannabis use disorder.

“The entanglement of substance use disorders and mental illnesses is a major public health issue, requiring urgent action and support for people who need it. As access to potent cannabis products continues to expand, it is crucial that we also expand prevention, screening, and treatment for people who may experience mental illnesses associated with cannabis use," said NIDA Director and study coauthor Nora Volkow, M.D. "The findings from this study are one step in that direction and can help inform decisions that health care providers may make in caring for patients, as well as decisions that individuals may make about their own cannabis use.”

Although there are many risk factors associated with schizophrenia, in this study, researchers sought to estimate the proportion of all schizophrenia cases that may be attributed to cannabis use disorder specifically. 

“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,” said Carsten Hjorthøj, Ph.D., 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.