Risk of Dementia in Individuals With Emergency Department Visits or Hospitalizations Due to Cannabis.

IMPORTANCE

Cannabis use is associated with short-term memory impairment and long-term changes in brain structure; however, little is known about whether disordered cannabis use is associated with an increased risk of a dementia diagnosis.

OBJECTIVE

To investigate the association between emergency department visits or hospitalizations (acute care encounters) due to cannabis and future dementia diagnosis.

DESIGN, SETTING, AND PARTICIPANTS: Population-based, retrospective, matched cohort study using health administrative data from Ontario, Canada, between 2008 and 2021 (with follow-up until 2022) including all individuals aged 45 to 105 years living in Ontario who were eligible and did not have a diagnosis of dementia at cohort entry (2 620 083 individuals excluded).

EXPOSURE

Individuals with incident acute care due to cannabis use, defined using International Classification of Diseases and Related Health Problems, Tenth Revision coding.

MAIN OUTCOMES AND MEASURES

We used cause-specific adjusted hazard models to compare new diagnoses of dementia (from a validated algorithm) between individuals with acute care due to cannabis use with (1) individuals with all-cause acute care (excluding cannabis), (2) the general population, and (3) individuals with acute care due to alcohol use.

RESULTS

The study included 6 086 794 individuals, of whom 16 275 (0.3%) had incident acute care due to cannabis use (mean age, 55.2 [SD, 8.3] years; 60.3% male). Annual rates of incident acute care due to cannabis use increased 5.0-fold in individuals aged 45 to 64 years (from 10.16 to 50.65 per 100 000) and 26.7-fold in individuals aged 65 years or older (from 0.65 to 16.99 per 100 000) between 2008 and 2021. Individuals with incident acute care due to cannabis use were at a 1.5-fold and 3.9-fold increased risk of dementia diagnosis within 5 years relative to individuals with all-cause acute care and the general population of the same age and sex, respectively (absolute rates of dementia diagnosis: 5.0% for cannabis-related acute care, 3.6% for all-cause acute care, and 1.3% in the general population). After adjustment for sociodemographics and chronic health conditions, individuals with acute care due to cannabis use remained at elevated risk relative to those with all-cause acute care (adjusted hazard ratio [aHR], 1.23; 95% CI, 1.09-1.39) and the general population (aHR, 1.72; 95% CI, 1.38-2.15). Individuals with acute care due to cannabis use were at lower risk than those with acute care due to alcohol use (aHR, 0.69; 95% CI, 0.62-0.76).

CONCLUSIONS AND RELEVANCE

Individuals with cannabis use severe enough to require hospital-based care were at increased risk of a new dementia diagnosis compared with those with all-cause hospital-based care or the general population. These findings have important implications considering increasing cannabis use among older adults.