Cannabis use disorder among young people linked to diagnosis of psychiatric disorders
Analysis of nearly 700,000 health records reveals age-related association between cannabis use disorder and subsequent psychiatric disorders diagnoses
A new study led by Johns Hopkins researchers found that young people with cannabis use disorder were more likely than young people with other substance use disorders to later be diagnosed with a psychiatric disorder. In contrast, adults with cannabis use disorder were significantly less likely to develop psychiatric disorders, compared to adults with other substance use disorders.
The study found that the relative risk of young people age 17 and under with cannabis use disorder was 52% higher for schizophrenia, 30% higher for recurrent major depression, and 21% higher for anxiety disorders, compared to young people with other substance use disorders. Adults with cannabis use disorder had lower relative risks for being diagnosed with a psychiatric disorder.
The findings highlight the question of whether excessive cannabis use, perhaps more than other substances, might alter brain development of young people, predisposing them to developing a psychiatric disorder.
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.
Products made from the Cannabis sativa plant have been used recreationally in the U.S. since at least the 1800s. Their popularity increased during alcohol prohibition in the 1920s and the counterculture movement in the 1960s. Today, cannabis use by adults age 21 and older is legal in 24 U.S. states and the District of Columbia. Surveys suggest daily use of cannabis is higher than alcohol consumption.
“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 first appeared in medical literature in the early twentieth century. In 1987, a study of more than 45,000 Swedish army recruits found that the use of cannabis at the time of conscription was associated with large increases in the risk of subsequent schizophrenia, especially when the cannabis use was heavy. Other studies since then have found similar associations.
For the study, the researchers analyzed nearly 700,000 U.S. medical records from a large commercial database. They identified patients who had been diagnosed with cannabis use disorder—a condition that implies relatively heavy cannabis use—but had not been diagnosed with other psychiatric disorders. They then matched these patients on measures such as age, sex, ethnicity, and income level, with patients who had been diagnosed with other, non-cannabis substance use disorders and did not have other psychiatric conditions. The researchers compared the rates of subsequent schizophrenia and other psychiatric diagnoses in these two patient groups—adults age 18 and older (691,806 patients) and one for those age 17 and under (49,586 patients).
The median age among patients with cannabis use disorder was 16 versus 15 among patients with other substance use disorders. About 10% of patients in the cohort of all substance use disorders were under age 12. The authors note that this aligns with reports from adult patients being treated for substance use disorder: 10.2% reported starting substance use at age 11 or younger.
Adults in the cannabis use disorder group had a 19% lower risk (0.34% vs. 0.42%) of subsequent schizophrenia compared to the group with other substance use disorders. Risks of subsequent psychosis, recurrent major depression, and suicide attempts were also lower in the cannabis-use group.
The results are consistent with the idea that heavy cannabis use predisposes young people to subsequent schizophrenia and some other psychiatric disorders that they might not develop otherwise. Thrul notes that this acceleration effect could make these illnesses seem less likely at later ages, thus appearing to lower the risk in adults, at least in relation to other recreational drugs.
Thrul cautions, however, that the causation might point in the other direction, with individuals who are innately more likely to develop certain psychiatric disorders to also have a greater tendency to self-medicate with cannabis, even before their mental health issues have become evident.
“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.
One of the paper’s limitations is that the database the researchers used relied on International Classification of Diseases ICD-10 coding by other physicians, so the researchers may not know the exact patient history that led to the diagnosis.
“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.
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