April 21, 2025 – Add cannabis to the list of things now linked to a heightened risk of dementia.
Cannabis users who visited the emergency room or were hospitalized were up to four times as likely as people in the general population to be diagnosed with dementia within five years, according to a large new study.
While the study can't say that cannabis use causes dementia – a progressive disease that affects memory, thinking, and language, along with emotions and behavior – its findings are compelling enough to capture attention from both the public and the medical community.
Here's what to know about those findings, what's still being investigated, and why it matters to you.
What the Study Found
The most well-known biological feature of dementia is the presence of brain plaques that kill neurons. Age is the biggest risk factor, but strong links have also been made to things like high blood pressure, diabetes, poor diet, heart and sleep problems, and lack of physical activity.
Published in JAMA Neurology, the study found that:
- Cannabis users who went to the ER were 23% more likely to be diagnosed with dementia within five years, compared with nonusers who also went to the ER.
- Among hospital patients, those who used cannabis had a 72% greater risk of dementia within five years, compared with cannabis abstainers.
- The rate of people seeking ER or hospital care with documented cannabis use skyrocketed between 2008 and 2021, increasing five-fold. The rate among people ages 65 and older increased nearly 27-fold.
Does This Research Apply to You?
The study only included Canadian adults ages 45 and older who had no prior dementia diagnosis. It's garnered a lot of respect in medical circles because of its size – more than 6 million people's health data was included, making the results more reliable than past, smaller marijuana studies.
But there are some important limitations and context to consider:
- Most people in the study were included for comparison purposes, and the number of cannabis users was only about 16,000. The average age among users was 55, and their age varied a lot. About 60% were men.
- The cannabis users were getting medical care for reasons related to their cannabis use – including mental and behavioral illness due to cannabis use, poisoning or adverse effects of cannabis or its derivatives, and cannabis addiction.
- About 5% of cannabis users in the study were diagnosed with dementia within five years, compared to 3.6% of people who went to the ER or hospital for other reasons. The rate of dementia in a general population comparison group was 1.3%.
- Looking 10 years after the ER or hospital visit, 19% of users were diagnosed with dementia, compared to 15% of nonusers who got the same level of medical care.
- Cannabis use was linked to a 31% lower risk of dementia within five years, compared to people who were treated in the ER or hospital due to alcohol use, the researchers found.
What's Still Being Investigated
There's still a lot we don't understand about the possible link between dementia and cannabis use. What researchers still don't know:
- Whether the link still exists for people who use cannabis without needing medical care
- How the complex interaction of genetics, lifestyle, and other health conditions combine with cannabis use to increase a person's risk of having dementia
The Bigger Picture
This is just the latest in a string of recent studies shedding long-awaited light on the health impacts of cannabis use.
A lack of scientific research has led many people to form their understanding of marijuana's health effects based on limited evidence from their own or others' experiences. Medical experts have long warned that the true health impacts of marijuana are largely unknown, and in recent years, some of the first rigorous studies have offered new information, including links between cannabis and:
- Cardiovascular problems, like strokes and heart attacks
- Early death
- Reduced brain function during tasks that involve mental skills
Those risks are along with the already well-established understanding that cannabis use is particularly risky among youths and young adults, whose brains are still developing. The American Psychiatric Association says there's evidence that cannabis use can speed up the start of mental illness, particularly in young adulthood. People with depression who use cannabis are at an increased risk of suicidal thoughts or attempts. Risks increase based on how much and how long a person uses.
Mental health support or help with emotional distress, alcohol, or drugs is available 24/7 by calling or texting 988, or you can visit 988lifeline.org.
