Youth cannabis disorder tied to later psychiatric diagnoses

A new Johns Hopkins-led study found that young people with cannabis use disorder were more likely than their peers with other substance use disorders to later receive a psychiatric diagnosis, while adults with cannabis use disorder were less likely than adults with other substance use disorders to develop psychiatric disorders, according to researchers.

The analysis, based on nearly 700,000 U.S. health records, adds to growing scientific scrutiny over how heavy cannabis use may affect younger users differently from adults.

Among young people age 17 and under with cannabis use disorder, the study found a 52% higher relative risk for schizophrenia, a 30% higher relative risk for recurrent major depression, and a 21% higher relative risk for anxiety disorders, compared with young people with other substance use disorders.

The findings raise fresh questions about whether excessive cannabis use may alter brain development in adolescents and increase vulnerability to later psychiatric illness.

The study was published online March 5 in the American Journal of Psychiatry.

“Is cannabis use a unique risk factor compared to the use of other substances such as alcohol, opioids, or cocaine? That’s the question we addressed in this study, and our findings suggest that that relative risk depends on the user’s age,” says study co-author Johannes Thrul, PhD, associate professor in the Department of Mental Health at the Bloomberg School.

Cannabis products made from the Cannabis sativa plant have been used recreationally in the United States since at least the 1800s, with wider popularity during alcohol prohibition in the 1920s and the counterculture movement of the 1960s, according to the press release.

Today, cannabis use by adults age 21 and older is legal in 24 U.S. states and the District of Columbia, while surveys suggest daily cannabis use now exceeds alcohol consumption, the release said.

“Much of our interest in this came from the recent legalization of recreational cannabis in Maryland, in 2023, and other states,” says Ryan Nicholson, MD, resident at Johns Hopkins University School of Medicine. “We wanted to understand cannabis-related psychotic disorders clinicians are seeing in the context of other substance-related psychotic disorders.”

The link between cannabis and psychosis has appeared in medical literature since the early 20th century, and the release cited a 1987 study of more than 45,000 Swedish army recruits that associated cannabis use at conscription with sharply higher risks of later schizophrenia, especially with heavy use.

For the new study, researchers analyzed nearly 700,000 U.S. medical records from a large commercial database.

They identified patients with cannabis use disorder, a diagnosis that implies relatively heavy cannabis use, and excluded those already diagnosed with other psychiatric disorders.

They then matched those patients by age, sex, ethnicity and income level with patients diagnosed with other, non-cannabis substance use disorders who also had no other psychiatric conditions.

The researchers compared subsequent rates of schizophrenia and other psychiatric diagnoses across two groups: adults age 18 and older, totaling 691,806 patients, and those age 17 and under, totaling 49,586 patients.

The median age among patients with cannabis use disorder was 16, compared with 15 among patients with other substance use disorders.

About 10% of patients in the cohort of all substance use disorders were younger than 12.

The authors said that figure aligns with reports from adults receiving treatment for substance use disorder, of whom 10.2% said they began using substances at age 11 or younger.

Among adults, the cannabis use disorder group had a 19% lower risk of subsequent schizophrenia than the group with other substance use disorders, with rates of 0.34% versus 0.42%.

Risks of subsequent psychosis, recurrent major depression and suicide attempts were also lower in the adult cannabis use disorder group, according to the study.

The researchers said the results are consistent with the idea that heavy cannabis use may predispose young people to schizophrenia and some other psychiatric disorders they might not otherwise develop.

Thrul said one possible explanation is an acceleration effect, in which cannabis-related harm surfaces earlier in life and makes such illnesses appear less likely at older ages relative to other recreational drugs.

He also cautioned that the causal relationship remains unresolved and may partly run in the opposite direction, with people already predisposed to psychiatric disorders turning to cannabis as self-medication before symptoms are formally recognized.

“There are still many unknowns on that question, but I would never recommend that teenagers use cannabis, especially not the high-potency cannabis products that are on the market now,” he says.

The paper also noted a key limitation: The database relied on International Classification of Diseases ICD-10 coding by other physicians, meaning the researchers may not know the exact patient history behind each diagnosis.

The study, “Association of Cannabis Versus Other Substance Use Disorders with Psychiatric Conditions: A Propensity-Matched Retrospective Cohort Analysis,” was co-authored by Ryan Nicholson, Una Choi, Ramin Mojtabai and Johannes Thrul.