Youth, Cannabis, and Mental Disorders: A 52% Higher Risk of Schizophrenia

The study compared the risk of mental disorders between people who use cannabis and those who use other substances. In adults, cannabis use was associated with a lower risk of several mental disorders. In young people, the opposite occurred: the risk was higher. Age and context of use appear to be decisive factors in these results.

This study sought to better understand how problematic cannabis use may be related to the development of mental disorders over time. Although there is already much discussion about the effects of cannabis on mental health, there are still important questions, especially when comparing its impact with that of other substances, such as alcohol or other drugs.

The researchers wanted to answer a central question: is the risk of developing problems such as depression, anxiety, or schizophrenia different between people who use cannabis and those who use other substances?

To investigate this, the authors used a large international database called TriNetX, which gathers information from millions of patients treated in health services. From this database, they selected people who had a diagnosis of problematic substance use, but who did not yet present any mental disorder at the beginning of the follow-up. This was important to ensure that the mental health problems analyzed actually arose later, and not before.

Researchers divided participants into different groups to make the comparison fairer and more detailed. They analyzed adults and children or adolescents separately. They also distinguished people who only had problematic cannabis use from those who used other substances, in addition to a third group that combined cannabis with other drugs. This division allowed them to observe important differences in age and usage patterns.

To avoid unfair comparisons, a statistical technique was used that basically "balances" the groups, ensuring that they are similar in several aspects, such as age, sex, health conditions, and other risk factors. In practice, this works like creating comparable groups, almost like a controlled experiment, even though it is a study based on existing data.

After forming these comparable groups, the researchers followed the patients over time to see how many of them developed mental disorders, such as schizophrenia, depression, anxiety, or psychotic disorders. This allowed them to observe not only whether these problems arose, but also how frequently in each group.

The results showed an interesting pattern. Among adults who used only cannabis, the risk of developing mental disorders was generally lower than among those who used other substances.

However, among children and adolescents, the scenario was different: The study found that the relative risk of young people aged 17 or younger 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.

Finally, when researchers analyzed adults who combined cannabis with other substances, they observed that, even in this case, the risk of several mental disorders was still lower than in people who used other drugs without cannabis.

The authors suggest that these differences may be related to the age at which use begins or to the fact that cannabis may influence the timing of the onset of certain mental disorders, especially in younger individuals.

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Association of Cannabis Use Disorder Versus Other Substance Use Disorders With Psychiatric Conditions: A Propensity-Matched Retrospective Cohort Analysis

Ryan C. Nicholson, Una E. Choi, Ramin Mojtabai, and Johannes Thrul

DOI:10.1176/appi.ajp.2025033

Abstract:

The authors compared the risk of mental disorders between patients with cannabis use disorder (CUD) and those with other substance use disorders (SUDs). The TriNetX Research Network was queried to identify patients with SUDs and no preceding mental disorders and compare 1) adult patients with CUD only versus those with other SUDs, 2) pediatric patients with CUD only versus those with other SUDs, and 3) adult patients with CUD plus another SUD versus those with comorbid noncannabis SUDs. Propensity score matching was performed on demographic characteristics and 24 risk factors or comorbidities. Subsequent diagnosis of schizophrenia and other common mental disorders was assessed. Compared to adults with other SUDs, those with noncomorbid CUD (N=345,903 for both cohorts) had a lower risk of schizophrenia (0.34% vs. 0.42%; relative risk [RR]=0.81, 95% CI=0.75, 0.88), depression (1.35% vs. 1.74%; RR=0.78, 95% CI=0.75, 0.81), and psychotic disorders (0.36% vs. 0.52%; RR=0.68, 95% CI=0.63, 0.73). Compared to pediatric patients with other SUDs, those with CUD (N=24,793 for both cohorts) had a higher risk of schizophrenia (0.29% vs. 0.19%; RR=1.52, 95% CI=1.06, 2.19), depression (1.65% vs. 1.27%; RR=1.30, 95% CI=1.13, 1.51), and anxiety disorders (8.13% vs. 6.71%; RR=1.21, 95% CI=1.14, 1.29). Compared to adult patients with other SUDs, those with CUD and a comorbid SUD (N=203,916 for both cohorts) had a decreased risk of schizophrenia (1.94% vs. 2.25%; RR=0.86, 95% CI=0.83, 0.90), depression (3.98% vs. 5.67%; RR=0.70, 95% CI=0.68, 0.72), bipolar disorder (4.23% vs. 5.60%; RR=0.76, 95% CI=0.74, 0.78), and anxiety disorders (16.20% vs. 21.36%; RR=0.76, 95% CI=0.75, 0.77). CUD-associated mental health risks varied by age and comorbid SUDs, possibly due to earlier onset of mental disorders in cannabis users or age-related differences in CUD effects.