By Amy Norton
PISCATAWAY, NJ – More people are landing in the hospital with cannabis-related problems—and for many, a mental health condition is the primary issue, according to a new study published in the Journal of Studies on Alcohol and Drugs.
The study, conducted in Arizona, found that between 2016 and 2021, cannabis-related hospital visits across the state rose by 20%. Among those visits, one quarter ended up with a primary diagnosis of a mental health condition, including bipolar disorder, depression, and psychotic disorder. That compared with only about 3% of visits unrelated to cannabis.
Overall, people with a cannabis-related hospital visit were nearly eight times as likely to have a primary diagnosis of a mental health disorder. And the link between the two grew stronger over the five-year study period.
The reasons for the rising rate of cannabis-related visits are unclear, according to lead researcher Madeline Meier, Ph.D., an associate professor of psychology at Arizona State University, in Tempe, Ariz.
But, she said, legalization of non-medical (recreational) cannabis use is not to blame: Arizona legalized non-medical use for adults in late 2020, with sales beginning in 2021—too late to explain the trends seen during the study period.
On the other hand, Meier said, medical use of cannabis was legal in Arizona throughout the study period. So it's possible that easier access to the drug is partly responsible for the trends her team found. Meier noted that when states have less-restrictive policies on medical cannabis—such as making it available in dispensaries rather than pharmacies—that can make it easier for any adult to get the drug.
The findings also raise other key questions: Why do so many people with cannabis-related hospital visits have a mental health condition, and why is the connection between the two growing stronger over time?
"There are many possible explanations, and this study can't address them," Meier said. But based on other research, she said, one possibility is that cannabis use led to mental health conditions in some people. Another is that some people were using cannabis to treat mental health symptoms—and that tendency increased over time.
If that's the case, Meier said, it points to a need for better public education. "I think it's important for people to be aware that the science on using cannabis to treat mental health problems is really not there yet," she said. "In fact, there is evidence suggesting that cannabis use can worsen mental health conditions, or even increase the risk of developing them."
The study also found some interesting patterns related to age: Older adults (age 65 and up) showed a bigger jump in cannabis-related hospitalizations between 2016 and 2021, versus other adults. And the growing tendency for those hospitalizations to be linked to mental health conditions was most pronounced among older adults.
That's not necessarily surprising, Meier said, given Baby Boomers' permissive attitudes about cannabis use. But, she added, older adults may need particular education about the potential risks of using the drug—including the fact it is much more potent (and potentially intoxicating) these days, compared with the cannabis of decades ago.
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Meier, M. H., Hummel, H. M., & Miller, M. L. (2025). Trends in cannabis-related hospitalizations in Arizona from 2016–2021 and associations with mental health-related hospitalizations. Journal of Studies on Alcohol and Drugs, 83(3). https://doi.org/10.15288/jsad.23-00379
