Adolescents show elevated risks of schizophrenia, depression and anxiety, while adults see comparatively lower rates, researchers find
By Bunmi Yekini
Young people with cannabis use disorder face a significantly higher risk of developing psychiatric conditions compared to peers with other substance use disorders, while the opposite appears true for adults, according to a new study led by researchers at Johns Hopkins University.
The study, published on March 5 in the American Journal of Psychiatry, found that individuals aged 17 and under with cannabis use disorder had a 52% higher risk of schizophrenia, a 30% higher risk of recurrent major depression, and a 21% higher risk of anxiety disorders compared to young people using other substances.
In contrast, adults with cannabis use disorder were less likely than those with other substance use disorders to later develop psychiatric conditions, including schizophrenia and psychosis.
Researchers said the findings raise concerns that heavy cannabis use may uniquely affect brain development in young people, potentially increasing vulnerability to mental health disorders.
“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,” said study co-author Johannes Thrul. “Our findings suggest that the relative risk depends on the user’s age.”
The research analysed nearly 700,000 U.S. medical records, comparing patients diagnosed with cannabis use disorder to matched individuals with other substance use disorders but no prior psychiatric diagnoses. The study included both adults and nearly 50,000 individuals aged 17 and under.
Among adults, the risk of schizophrenia was 19% lower in those with cannabis use disorder compared to other substance users. Risks of depression, psychosis and suicide attempts were also lower in this group.
Lead author Ryan Nicholson said the study was partly motivated by the recent expansion of cannabis legalisation in the United States, including in Maryland in 2023, and a growing number of cannabis-related psychiatric cases observed by clinicians.
The link between cannabis use and psychosis has been documented for decades, including a landmark 1987 study of Swedish military recruits that found heavy cannabis use was associated with a higher risk of schizophrenia.
Researchers cautioned that the new findings do not establish causation. It remains unclear whether cannabis use contributes to psychiatric disorders, or whether individuals predisposed to such conditions are more likely to use cannabis.
“There are still many unknowns,” Thrul said, adding that he would not recommend cannabis use among teenagers, particularly high-potency products.
The study also noted limitations, including reliance on diagnostic coding in medical records, which may not fully capture patients’ histories.
The authors said further research is needed to better understand how cannabis affects mental health across different age groups.