New Study: Increased Risk of Dementia in People With Marijuana Use Requiring Hospital-Based Care

A large observational study from Ontario, Canada, focuses attention on an increased risk of dementia in people with marijuana (cannabis) use that is intensive enough to require hospital-based care. Published in JAMA Neurology in April 2025, the study found a strong association between emergency-department visits or hospitalization due to cannabis use and a new dementia diagnosis, which emerged years later.[1]

As marijuana use is increasing overall and especially among older adults, the findings have “important implications,” as the authors note, in part because older adults are already at increased risk of dementia because of their age.

Background on marijuana use and dementia

As discussed in the February 2025 issue of Worst Pills, Best Pills News, the marijuana plant has a long history of medicinal and recreational use. The plant, which is typically dried, ignited and smoked (combusted and inhaled), contains over 500 chemical substances, including cannabidiol (CBD) and the primary psychoactive ingredient delta-9-tetrahydrocannabinol (Δ9-THC).[2]

The FDA has approved two marijuana-derived oral products for narrow indications: dronabinol (MARINOL and generics) for nausea due to cancer chemotherapy or for anorexia (loss of appetite) associated with HIV/AIDS, and CBD (EPIDIOLEX) for some rare childhood seizures. Although legalized in some states for medical or recreational use, marijuana is illegal at the federal level.[3]

In May 2024 the Drug Enforcement Administration (DEA) proposed a rule that would move marijuana from Schedule I (a classification for substances with no accepted medical use and high abuse potential) to Schedule III (a classification for drugs or other substances with an intermediate potential for physical or psychological dependence). As of September 2025, the DEA classification of marijuana had not changed.

As of 2024, about 80% of Americans lived in a county with a marijuana retail outlet and 22% of the population reported past-year marijuana use.[4] By comparison, past-year use of cannabis in adults aged 65 years or older increased from less than 1.0% in 2005 to 4.2% in 2018.[5] Between 2021 and 2023, the prevalence of past-month cannabis use increased from 4.8% to 7.0%, according to a June 2025 report in JAMA Internal Medicine. The study used nationally representative data from the National Survey on Drug Use and Health and included about 15,700 adults.[6]

Evidence that marijuana use may have negative effects on brain health, and sometimes lead to dementia later in life, comes from studies that have directly measured brain function and structure, including studies that assessed memory, attention, and the physical configuration of the brain’s neural architecture and interconnections.[7]

The JAMA Neurology study

The 2025 JAMA Neurology study was based on health administrative data collected between 2008 and 2021 in the Canadian province of Ontario, with follow-up until 2022. Of the initial cohort of more than 6 million individuals, 16,275 (0.3%) had new acute care related to cannabis use within three years of their study index date (the date from which their follow-up began to look for an association with incident dementia). Importantly, acute care due to cannabis use was defined as care involving an emergency-room visit or a hospitalization, thus likely more serious than acute care at an outpatient visit. There were three comparison groups: individuals with all-cause acute care (excluding cannabis), the general population, and individuals with acute care due to alcohol use.

After matching people on factors such as age, sex, and type of acute-care visit, the researchers further adjusted for differences in sociodemographic variables and comorbidity indicators, including those characterizing the presence or absence of mental health or substance abuse disorders or 13 other chronic conditions. These latter adjustments were important because people in the cannabis group had markedly higher baseline rates of mood disorders and opioid and alcohol use disorders, whereas those in the all-cause acute-care group had markedly higher baseline rates of other chronic health conditions such as hypertension, cancer and diabetes.

Over 10 years of follow-up, 18.8% of people with cannabis-related acute care were diagnosed with dementia compared with 14.9 % of people in the all-cause acute-care group. This difference was significant in the fully adjusted statistical model, which suggested an overall increased risk of dementia of approximately 23% among people with cannabis-related acute care. By comparison, in the fully adjusted statistical model, the increased risk of dementia was 72% higher among people with cannabis-related acute care than in the general population but about 31% lower than the population who experienced alcohol-related acute care.

The study also found that between 2008 and 2021, the annual rate of incidents of cannabis-related acute care increased by 26.7-fold in people aged 65 years or older and only by 5.0-fold in those aged 45 to 64 years. As compared with the 2008 to 2014 period, the increased rate of visits for cannabis-related acute care accelerated between 2015 and 2021.

What You Can Do

The use of marijuana or related CBD- or THC-containing products for medical or nonmedical use is increasingly an individual choice. The new study calls attention to the elevated risk of a dementia diagnosis associated with hospital-based care for cannabis use as well as the increased risk of dementia related to acute care for alcohol use, which was well known. It also highlights the large increases in cannabis use among older adults, who are already at greater risk of dementia.

Be aware that heavy cannabis use is an emerging risk factor for dementia later in life and years after the cannabis use has occurred. During medical visits, disclose your use of marijuana and related products as well as your use of alcohol. Discuss the potential adverse health effects and formulate a plan to minimize the risks.
 

References

[1] Myran DT, Pugliese M, Harrison LD, et al. Risk of dementia in individuals with emergency department visits or hospitalizations due to cannabis. JAMA Neurol. 2025;82(6):570-579.

[2] Marijuana (cannabis) use: an update from the FDA. Worst Pills, Best Pills News. February 2025. https://www.worstpills.org/newsletters/view/1646. Accessed August 4, 2025.

[3] Drug Enforcement Administration. Proposed rule: Schedules of controlled substances: rescheduling of marijuana. May 21, 2024. https://www.regulations.gov/document/DEA-2024-0059-0001. Accessed August 4, 2025.

[4] National Academies of Sciences, Engineering, and Medicine. Cannabis Policy Impacts PublicHealth and Health Equity. Washington, DC: The National Academies Press. 2024. https://doi.org/10.17226/27766. Accessed August 4, 2025.

[5] Han BH, Yang KH, Cleland CM,et al. Trends in past-month cannabis use among older adults. JAMA Intern Med. 2025;185(7):881-883.

[6] Ibid.

[7] Myran DT, Pugliese M, Harrison LD, et al. Risk of dementia in individuals with emergency department visits or hospitalizations due to cannabis. JAMA Neurol. 2025;82(6):570-579.