Researchers in Ontario, Canada have found a troubling connection between severe cannabis use among adults 45 and older and increased dementia diagnoses. 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."
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.