Mental health risks of cannabis addiction depend heavily on age

As cannabis legalization spreads, new research reveals that the mental health risks tied to a cannabis addiction depend heavily on a patient’s age. A recent study published in the American Journal of Psychiatry found that adolescents with a cannabis use disorder are more likely to develop psychiatric conditions compared to peers addicted to other drugs, while adults face a comparatively lower risk. These results point to a need for age-specific approaches to drug education and public health policies.

Products made from the Cannabis sativa plant have a long history in the United States, with recreational use dating back to at least the 1800s. Consumption climbed during alcohol prohibition in the 1920s and the counterculture movement of the 1960s, continuing to rise as states legalize the drug. As of early 2025, recreational cannabis is legal in 24 states and the District of Columbia, and surveys suggest that daily cannabis use now outpaces daily alcohol consumption.

With expanded access, doctors are treating more cases of cannabis use disorder, a condition where a person cannot stop consuming the drug even when it causes health or social problems. Medical literature from the early twentieth century first hinted at a connection between cannabis and psychosis, a disconnection from reality often involving hallucinations. Later, a 1987 study of more than 45,000 Swedish army recruits demonstrated that heavy cannabis use at conscription was linked to large increases in the risk of subsequent schizophrenia.

Ryan C. Nicholson, a medical resident at the Johns Hopkins University School of Medicine, led a research team to investigate the specific psychiatric differences between cannabis and other drugs. “Much of our interest in this came from the recent legalization of recreational cannabis in Maryland, in 2023, and other states,” Nicholson said. “We wanted to understand cannabis-related psychotic disorders clinicians are seeing in the context of other substance-related psychotic disorders.”

Johannes Thrul, an associate professor at the Johns Hopkins Bloomberg School of Public Health, co-authored the study. “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,” Thrul said
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To answer these questions, the research team analyzed nearly 700,000 medical records from the TriNetX commercial database. They identified patients diagnosed with a substance addiction who had no previous history of mental illness. To ensure fair comparisons, the researchers used a statistical technique called propensity score matching.

This method pairs individuals from different groups who share similar life circumstances and health histories. The team matched patients based on factors such as age, sex, ethnicity, and income level. By comparing these matched groups, the researchers could isolate the effects of specific drug addictions on later mental health.

The team tracked the patients’ medical records forward in time to look for new psychiatric diagnoses. The data revealed clear differences based on the age of the patients, who were divided into a group of 691,806 adults and a group of 49,586 youths age 17 and under. Among the pediatric patients, the median age for those with a cannabis addiction was 16, compared to 15 for youths addicted to other substances.

Notably, about 10 percent of the patients across all the addiction categories were under age 12. The researchers noted this aligns with other clinical reports showing that roughly 10.2 percent of adult patients being treated for an addiction started using drugs at age 11 or younger. These early exposures provided a foundation for exploring long-term health outcomes.

The health outcomes for pediatric patients indicated a distinct vulnerability to mood and psychotic disorders. Adolescents with a cannabis addiction had a 52 percent higher relative risk of being diagnosed with schizophrenia than adolescents addicted to other substances. They also faced a 30 percent higher risk for recurrent major depression and a 21 percent higher risk for anxiety disorders.

Conversely, adults addicted solely to cannabis had a lower risk of developing most mental health conditions compared to adults addicted to other drugs. The cannabis group showed a 19 percent lower risk for schizophrenia, at 0.34 percent compared to 0.42 percent for the other substance group. Risks of subsequent psychosis, recurrent major depression, and suicide attempts were also lower in the adult cannabis group.

The researchers also examined adults who struggled with multiple drug addictions at the same time. They compared patients addicted to cannabis plus another drug against patients addicted to multiple non-cannabis drugs. Similar to the single-substance adult group, the patients with a combined cannabis addiction showed lower rates of schizophrenia, depression, and bipolar disorder.

When breaking down the adult data by specific substances, more nuanced patterns emerged. Compared specifically to patients with an alcohol addiction, the cannabis group had a lower risk of depression and psychotic disorders. Compared to patients addicted to cocaine, the cannabis group had lower rates of schizophrenia and depression, but higher rates of anxiety.

The comparison with opioid addiction yielded another specific variation. Adults with a cannabis addiction had a slightly higher risk of developing schizophrenia than adults with an opioid addiction. Yet, those same cannabis users had lower rates of depression and anxiety than the opioid users.

The study authors proposed a few biological explanations for the elevated risks seen in teenagers. The human brain contains a communication network called the endocannabinoid system, which helps regulate mood, memory, and brain development. During adolescence, the receptors for this system reach their highest concentration in areas of the brain responsible for complex thinking. Introducing cannabis during this critical developmental window might alter the way the prefrontal cortex matures.

The results suggest that heavy cannabis use might predispose young people to schizophrenia and other psychiatric disorders they might not develop otherwise. Thrul notes that this acceleration effect could make these illnesses seem less likely at later ages. This phenomenon would make it appear as though the risk is lower in adults in relation to other recreational drugs.

Alternatively, Thrul cautions that the cause and effect might point in the opposite direction. Individuals who are innately more likely to develop certain psychiatric disorders might have a greater tendency to self-medicate with cannabis. They may seek out the drug before their mental health issues become clinically evident.

Like all observational studies, this research comes with certain limitations. The database relies on diagnostic coding by various physicians, which means the researchers do not know the exact patient history that led to each diagnosis. The electronic health records also lack details about the exact type and potency of the cannabis consumed.

Future research will need to track exactly how much cannabis people consume and measure the chemical concentrations in those products. Scientists hope to use brain imaging technology to watch how long-term cannabis exposure changes the physical structure of the developing brain. Pathology studies could also help map the exact cellular changes that occur.

In the meantime, public health officials can use this data to refine how they talk to teenagers about drug use. “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,” Thrul said.

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