Adolescents with cannabis use disorder have higher risks for later development of psychiatric disorders

The ongoing legalization of cannabis in the United States has elicited cheers, boos and a host of questions. How much is safe? Isn’t it just a plant? What are the long-term effects of chronic use?

In a recent study, Johns Hopkins University researchers looked into how often the diagnosis of a psychiatric disorder follows heavy cannabis use versus the use of substances such as alcohol or other drugs. The results were surprising.

“The risks [of later psychiatric disorders] in adolescents with heavy cannabis use go beyond that of other substances—I wasn’t expecting that,” says Johannes Thrul, an associate professor in the Department of Mental Health at the Bloomberg School of Public Health and a co-author of the study. “The other surprising thing was that adults had a lower risk.”

A conversation between two Johns Hopkins medical students on a psychiatry rotation led to the study. “The medical team told me they had anecdotally been noticing an increase in what they suspected were cannabis-related psychiatric disorders,” says Una Choi, SOM ’24, an author on the study and now a medical resident at Brigham and Women’s Hospital of Harvard Medical School in Boston.

After a literature review that showed a dearth of studies comparing cannabis to other substances, “I wanted to see if we could do that comparison,” says Ryan Nicholson, BSPH ’24 (MPH), SOM ’25, the study’s first author and now a medical resident at Johns Hopkins Hospital.

The investigation was Nicholson’s capstone project for his master’s degree in public health, and the results were sent off for publication after encouragement from Thrul, Nicholson’s adviser at the time.

The study appears in the American Journal of Psychiatry.

The researchers examined nearly 700,000 medical records from the TriNetX research network, looking for associations between cannabis and other substance use disorders and a subsequent diagnosis of a psychiatric disorder.

While the researchers could not access details on quantities, frequency or types of products used, the term “use disorder” implies heavy use, says Thrul. The researchers divided the results by age, examining a pediatric set of patients ages 17 and younger and an adult set of patients.

Renee Johnson, a professor in the Bloomberg School, praised the research approach. “Rather than looking at no substance use as the comparator, this study enables more of an apples-to-apples comparison. You could use this as an example of strong study design in an epidemiology class,” she says.

The study showed that adolescents with cannabis use disorder had higher risks for later development of psychiatric disorders—including schizophrenia (52% higher), depression (30% higher) and anxiety (21% higher)—compared with adolescents who used other substances.

Adults appeared to have lower risks, but it’s unclear whether this is an actual protective effect of cannabis or if adults with psychiatric disorders were left out of the study because their psychiatric diagnoses came before their substance use disorders.

The researchers and authors point out the possibility that cannabis interferes uniquely with adolescent brain development and thus confers greater risks for subsequent psychiatric disorders, especially schizophrenia.

Another alarming possibility, says Brendt Stier, an affiliate professor of psychology at Loyola University who teaches a graduate-level pharmacology course, is that symptoms of an early, undiagnosed psychiatric disorder, such as social withdrawal and depression, may cause an adolescent to self-medicate with cannabis, which can then lead to an increased risk of schizophrenia, for instance.

Would the schizophrenia have developed without the cannabis? “It’s difficult to tease this apart,” says Thrul, “but what is clear from this study is that the risk of cannabis use disorder differs by age, and underage use is not recommended.”

With cannabis legal for medical use in 40 U.S. states and recreationally in 24, policies and legislation are constantly evolving, making studies like this one even more important.

“Legalization has resulted in more people thinking cannabis isn’t dangerous, that it’s just a harmless ‘herb,'” says Carol Vidal, associate professor of psychiatry and behavioral sciences at Johns Hopkins. Stier explains that much of the cannabis on the market today isn’t the natural product it once was. “It’s designer pot,” he says, “grown in controlled conditions and bred for high potency.”

Johnson describes the challenge of effective public health messaging to adolescents: “With tobacco, young people were told, ‘You are a dollar sign to corporations,’ and it resonated. It’s harder to do that with cannabis because it is associated with counterculture and small business.” However, with the proliferation of smoke shops and dispensaries owned by conglomerates, that association is starting to fade.

While the study shows higher risks in adolescents with cannabis use disorder, Thrul says that in an ideal world, the positives of legalization—medical relief and less incarceration, especially in communities of color—would exist within a solid public health framework that would test the products and prevent underage use.

“We need nuance in a space where cannabis has been completely demonized or deemed a wonder drug and extremely beneficial,” he says. “The reality is in the shades of gray.”

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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