People who required emergency department (ED) or acute hospital care for cannabis use may have an increased risk of a subsequent dementia diagnosis, a retrospective matched cohort study of 6 million people in Canada suggested.
Among adults ages 45 years and older with no history of dementia, those who needed acute care due to cannabis use had a 1.5 times higher risk of a new dementia diagnosis within 5 years compared with patients who had an all-cause acute care encounter (absolute risk 5% vs 3.6%), reported Daniel Myran, MD, MPH, of the University of Ottawa in Canada, and co-authors.
The risk of a new dementia diagnosis for people who needed acute care due to cannabis use was 3.9 times higher than that of the general population (absolute risk 5% vs 1.3%).
After adjusting for sociodemographic variables and chronic health conditions, people requiring acute care due to cannabis use still had a higher risk of dementia than those with all-cause acute care (adjusted HR 1.23, 95% CI 1.09-1.39) and the general population (adjusted HR 1.72, 95% CI 1.38-2.15), Myran and colleagues reported in JAMA Neurology.
The risk of dementia among those who needed acute care due to cannabis use was lower than that of people who needed acute care due to alcohol use (adjusted HR 0.69, 95% CI 0.62-0.76).
Long-term or heavy cannabis use has been associated with cognitive problemsopens in a new tab or window in midlife. Imaging studies also have shown structural changesopens in a new tab or window in the brains of people who regularly use cannabis.
"Regular cannabis use might directly increase the risk of dementia through changes in brain structure," co-author Colleen Webber, PhD, of the Ottawa Hospital Research Institute, said in a statement.
"It's also possible that regular cannabis use increases the risk of other established risk factors for dementia, including high blood pressure, head trauma and other injuries, and a higher risk for depression and social isolation," she observed.
The study included 6,086,794 Canadians ages 45 years and older from Ontario who had no history of dementia when they entered the cohort between 2008 and 2021.
During this time period, the annual rates of incident acute care due to cannabis use increased by five times in people ages 45-64 years (from 10.16 to 50.65 per 100,000), and by nearly 27 times in people 65 years and older (from 0.65 to 16.99 per 100,000).
A total of 16,275 people (0.3%) in the study had incident acute care due to cannabis use. Their mean age was 55.2 years, and 60.3% were male. Most (76.4%) received care in the ED, and 23.6% had in-hospital care.
A matched analysis included 15,120 people with cannabis-related acute care and 125,704 people with all-cause acute care. The primary outcome was a diagnosis of dementia, including Alzheimer's disease, identified using a validated algorithm and administrative data. Median follow-up was 4 years.
Research about the epidemiological association between cannabis use and dementia is limited and results have been mixed, Myran and co-authors noted.
"Adding to the literature, we present the largest study to date, to our knowledge, on the longitudinal association between cannabis use leading to an ED visit or hospitalization and dementia diagnosis," they wrote.
"We also observed large increases in the incidence of acute care for cannabis use in older adults over time, with most of the increases starting in 2015, coinciding with the liberalization of medical cannabis in 2014 and the Canadian federal government's commitment to the legalization of nonmedical cannabis in December 2015 (which was implemented in October 2018)," the researchers pointed out.
The study had several limitations, Myran and colleagues acknowledged. It did not examine patterns of cannabis use that did not require acute medical care, they noted.
Importantly, the findings do not show that cannabis use causes dementia, they added. Residual confounding and reverse causation may have influenced results.
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