Individuals with an emergency department (ED) visit or hospitalisation due to cannabis were at 23% and 72% greater risk of a new dementia diagnosis within five years compared to individuals with an ED visit or hospitalisation for any other reason or the general population, according to a new study published in JAMA Neurology.

"Long-term and heavy cannabis use has been associated with memory problems in midlife along with changes in brain structure associated with dementia," says Dr. Daniel Myran, a Canada Research Chair in Social Accountability at the University of Ottawa, ICES Adjunct Scientist, Investigator at the Bruyère Health Research Institute, and Associate Scientist at The Ottawa Hospital.

"We set out to estimate the risk of being diagnosed with dementia in a group of people whose cannabis use resulted in a visit to the emergency room or required hospitalisation for treatment."

The study included 6 million adults aged 45 years or older from Ontario, Canada, who had no history of dementia when they entered the study cohort between 2008 and 2021. The individuals were followed until 2022.

Health data held at ICES were used to compare new diagnoses of dementia for individuals with patterns of cannabis use that required acute care, defined as a visit to the emergency department (ED) or hospitalisation. They were compared to three groups: 1) individuals with an all-cause acute care visit; 2) the general population; and 3) individuals with acute care due to alcohol use.

The authors make two cautions about the study findings. First, while they observed an association between patterns of cannabis use severe enough to lead to an acute health care visit, they did not examine patterns of cannabis use that did not require acute medical care. Second, the findings do not show that cannabis use causes dementia.

While evidence on the association between cannabis use and dementia continues to increase, the authors highlight potential mechanisms through which cannabis might result in dementia.

"Regular cannabis use might directly increase the risk of dementia through changes in brain structure. 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," says co-author Dr. Colleen Webber, Scientist at the Bruyère Health Research Institute.

"While we collectively need more research to better understand potential risks of regular cannabis use on cognition and dementia, we hope these findings can inform discussion between patients and health care providers," says Myran.