Study claims cannabis-related hospital visits for older adults increases dementia odds

A cannabis plant approaching maturity is photographed at the CannTrust Niagara Greenhouse Facility during the grand opening event in Fenwick, Ont., on Tuesday, June 26, 2018. THE CANADIAN PRESS/ Tijana Martin

Cannabis users who ended up in a hospital or emergency care were more likely to develop dementia within a decade, according to a new Canadian study – though researchers stress their claims show an association, not proof that the drug was the cause.

Published in JAMA Neurology on Monday, the study suggests that individuals aged 45 or older who had an emergency department (ED) visit or hospitalization due to cannabis use were at a higher risk of being diagnosed with dementia within the next five to 10 years.

When it comes to understanding how cannabis may affect long-term brain health, especially in older adults, Daniel Myran says the research is only the beginning.

The Ottawa-based public health physician and lead author of the study spoke with CTVNews.ca Tuesday to unpack the findings—and the questions that remain.

“We were interested in a different approach,” Myran said. “There’s a growing number of studies that look at brain imaging or memory testing for people who use cannabis, and those by design are often quite small – hundreds or a few thousand people who participate in the study, because it’s very expensive and intensive.”

Instead, Myran’s team turned to Ontario’s population-wide health care data, tracking more than six million people from 2008 to 2011 aged 45 and older with no history of dementia. By focusing on individuals who had an emergency or hospital visit for cannabis-related issues, they could study patterns at scale.

The trade off, Myran says, is that they lacked important lifestyle data.

“You don’t know how long people have been using cannabis, or how they use cannabis, and we don’t know other risk factors for dementia like smoking,” he said.

Cannabis use in older adults

Myran emphasizes the dramatic shift in cannabis consumption patterns.

“If you look back over the past 15 years, there really has been a very large increase in North America in cannabis use in middle-aged and older adults,” he said.

Among Ontario’s 15 million residents, past-year cannabis uses in adults aged 50 years or older increased from 5.4 per cent in 2010 to 21.8 per cent in 2023, according to the study.

Myran says one of the big factors in this age group is for potential medical use.

“People are hearing it might be good for pain or for sleep or for anxiety, and they’re interested in trying it to see whether or not there are benefits,” Myran said.

Increased risk of dementia

To better understand what the cannabis data means, the study included comparisons. One group included people who showed up in emergency care for any reason other than cannabis. Another comparison was to people who had an ED visit due to excessive alcohol, which Myran says is an established risk factor for dementia.

The study claims that individuals who required acute care for cannabis use were 23 per cent more likely to be diagnosed with dementia within five years and 72 per cent more likely over a 10-year period.

This is in comparison to the general population and individuals who had an ED visit or hospitalization for any other reason.

Among those studied,16,275 individuals had at least one emergency department visit or hospital stay due to cannabis use. Nearly 60 per cent of those surveyed were male.

The data showed that five per cent of individuals in the cannabis group were diagnosed with dementia within five years, rising to nearly 19 per cent by 10 years.

By comparison, only 3.6 per cent of individuals who were hospitalized for non-cannabis reason were diagnosed with dementia within five years and 14.8 per cent within 10 years.

As for the general population, 1.3 per cent were diagnosed within five years and 5.5 per cent within 10 years.

The annual rate of first-time emergency visits for cannabis-related use among adults 65 and older increased nearly 27 times over the study period, while the annual rate of people over 45 with a first-time emergency care visit for cannabis use increased five times over the study period.

Although the study says both cannabis and alcohol users showed elevated risks compared to the general population, the risk of dementia was somewhat lower in the cannabis group than in the alcohol group.

However, researchers caution that this does not imply cannabis is safer, only that both substances appear to contribute to cognitive risk in different ways.

While most people would accept that excessive drinking isn’t good for cognition, Myran says cannabis doesn’t have that same association in public perception. Their findings suggest that maybe it should.

Cautions and next steps

The authors of the study are careful to emphasize that the findings show an association, not direct causation.

“This isn’t a causal study,” Myran says, “This is not a study saying someone who’s using cannabis and frequently, a few times a year, once a month, is at this very large increased risk of dementia. That’s not what we studied.”

Myran says the important thing to note is that existing research raises caution on regular long-term cannabis use and its impact on memory, cognitive function and increased risk of dementia. If Canada wants clearer answers, Myran believes the next step is investment in long-term research.

“(For the) people who are recruited into a study, you have (to have) data on their patterns of cannabis use, other risk behaviours, health patterns followed over time,” he said.