Can your cannabis use increase your risk of developing dementia? That's what a new study is suggesting.
Researchers in Ontario, Canada have found a troubling connection between severe cannabis use among adults 45 and older and increased dementia diagnoses. Here's what you need to know about this growing field of research and how to keep your brain sharp.
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Dementia Diagnoses Are Higher Among Heavy Cannabis Users
The new study, published April 14, 2025 in JAMA Neurology, examined the health data of over 6 million adults age 45 and older living in Ontario from 2008 to 2021.
It zeroed in on those who had "incident acute care due to cannabis use." Meaning: If a person's THC use led to a medical emergency, they were included in the analysis; Casual or moderate users were not.
The researchers found that middle-age and older adults who were hospitalized or went to the ER because of their heavy cannabis use had a much higher risk of being diagnosed with dementia within the next 5 years than those of the same age and sex.
Specifically, this group had a 3.9 times greater risk of developing dementia than the general population, and a 1.5 times higher risk than those who were hospitalized for other reasons.
"This doesn't mean cannabis causes dementia," noted lead study author Daniel T. Myran, MD, MPH, in the study. "But it suggests that problematic use—severe enough to require hospital care—may be a warning sign or contributing factor."
The Cannabis-Dementia Link Has Mixed Results
This latest study is part of a growing body of research about THC and its effects on the brain.
While some studies show the habit may actually help manage agitation or anxiety in people already diagnosed with dementia, others suggest long-term use may potentially lead to memory issues or cognitive decline.
For instance, in 2022, Madeline Meier, PhD, an associate professor of psychology at Arizona State University, found through her research that "long-term cannabis users—people who have used cannabis from 18 or 19 years old and continued using through midlife—showed cognitive deficits compared with non-users... But people who used infrequently or recreationally in midlife did not show as severe cognitive deficits."
Further studies are needed to make any drastic conclusions, but for now, the current scientific evidence suggests that cannabis can affect people differently. And while not all use is harmful or necessarily linked with dementia, factors like how long you've been using the drug, when you started, and the severity of your habit can influence any side effects.
This new study, for example, suggests that THC should be used responsibly—especially in midlife and beyond.
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What You Need to Know
According to the CDC, cannabis is "the most commonly used federally illegal drug in the United States." The latest stats from 2021 show that 52.5 million people, or about 19% of Americans, have used it at least once.
With 24 states and the District of Columbia having legalized cannabis for medical or recreational use, the practice is becoming more and more common. To make sure your habits are healthy, experts say moderation and mindfulness are key.
If you're over 45 or have other health conditions, you should talk to your doctor before using THC. Plus, you should know the warning signs of a problematic habit, which include needing higher doses and continuing to use it despite negative consequences (like ER visits).
The CDC also warns on its site: "Cannabis use directly affects the parts of the brain responsible for memory, learning, attention, decision-making, coordination, emotion, and reaction time."
It's not suitable for anyone under the age of 18 or those who are pregnant or breastfeeding.
