Although cigarette use is declining among middle-aged people in the United States, cannabis use is increasing.
Cannabis smoke, like tobacco smoke, is linked to an increased risk of cancer and lung damage.
Now, a large-scale study has linked heavy cannabis use with an increased risk of dementia.
People aged over 45 who needed acute hospital care due to cannabis use had a 72% greater risk of receiving a dementia diagnosis within 5 years than the general population.
The National Institute on Drug Abuse reports that, in the United States, cannabis use among adults aged 35-50 reached an all-time high in 2022. Some 28% of people reported having used it during the previous year, compared with 13% in 2012.
Negative health effects from cannabis are more likely with heavy use. Habitual cannabis smoking (long-term, more than once a day) has been linked to cancers of the lungs, mouth and throat, as well as cognitive impairment, and even psychosis.
And acute effects, such as cyclic nausea and vomiting along with hot bathing and chronic cannabis use (cannabinoid hyperemesis syndrome), impaired coordination and performance, anxiety, suicidal ideation, and psychotic symptoms, can lead to emergency room visits or hospitalization.
Now, a study of 6 million people aged over 45 has found that those who have needed acute care after using cannabis had an increased risk of developing dementia in the 5 or 10 years following hospital attendance.
The Canadian study, which appears in JAMA Neurology, suggests that those with cannabis use severe enough to require hospital care are almost four times as likely to receive a dementia diagnosis within 5 years as the general population.
Steve Allder, MD, consultant neurologist at Re:Cognition Health, not involved in the study, told Medical News Today that:
“This is a landmark study due to its large sample size (over 6 million people) and longitudinal design. By examining dementia outcomes over this period, the researchers were able to provide insights into the long-term cognitive risks of cannabis use serious enough to result in emergency or hospital care.”
Acute cannabis use-linked care linked to higher dementia risk
The study, which ran from 2008 to 2021, included a total of 6,086,794 people. All were over 45 years old, with a mean age of 55.2 years, at the start of the study, and had no history of dementia.
The researchers noted that, between 2008 and 2021, annual rates of acute care due to cannabis use increased greatly, from about seven to 38 per 100,000 people. For people aged 45-64, annual incident acute care increased fivefold, and for those aged 65 and over there was a 26.7-fold increase.
A total of 16,275 people (0.3%) required acute hospital care due to cannabis use during the study.
At the 5-year point, 5% of those with acute care for cannabis, 3.6% of those with all-cause acute care, and 1.3% of the general population had been diagnosed with dementia.
Those needing acute care for cannabis use were 3.9 times as likely as the general population to receive a dementia diagnosis during the following 5 years. After 10 years,18.6% of those with cannabis use-related acute admissions had been diagnosed with dementia.
However, the researchers note that the risk of dementia diagnosis following a cannabis admission was lower than for those needing acute care for alcohol abuse.
And Rebecca Edelmayer, PhD, Alzheimer’s Association vice president of scientific engagement, cautioned that: “Alzheimer’s disease and other dementias are very complex and have many risk factors. We need to look at dementia risk from all angles to truly understand it.”
Why might cannabis increase dementia risk?
Previous studies have suggested negative cognitive effects from regular use of cannabis, particularly on working memory, attention and decision making.
So a potential link to dementia is not surprising. Allder suggested a number of mechanisms that might explain the link, including:
neurotoxicity, as high concentrations of tetrahydrocannabinol (THC) may damage neurons or interfere with synaptic pruning and neurogenesis, especially in aging brains
vascular effects — cannabis use has been linked to increased risk of hypertension and cerebrovascular incidents like stroke — both known risk factors for dementia
mental health links — heavy cannabis users often have higher rates of depression, anxiety, or psychotic disorders, which are independently associated with cognitive decline
head injuries, since cannabis intoxication can increase the risk of falls or accidents, leading to traumatic brain injuries — a strong contributor to dementia risk.
However, he told MNT that, while “cannabis might not directly ‘cause’ dementia, […] it contributes to a complex web of risks including vascular, psychological and neurological, which together elevate the likelihood of dementia diagnosis.”
The study authors added a note of caution about their observed association, noting that people requiring acute care for cannabis use were more likely to have other risk factors for dementia, such as tobacco or alcohol use, than the general population.
Brain changes could explain link between dementia risk and heavy cannabis use
While this observational study cannot draw conclusions about a causative effect of cannabis, brain changes observed in people who use the substance are similar to those seen in dementia, as Allder explained:
“Tetrahydrocannabinol (THC), the psychoactive component of cannabis, affects the hippocampus which is crucial for memory formation. Long-term exposure to THC has been linked to reduced hippocampal volume, which is also a hallmark of Alzheimer’s disease.”
“In addition,” he told us, “chronic cannabis users may show reduced grey matter density in brain areas responsible for executive function, emotion regulation and memory.“
“Cannabis use may also impair neuroplasticity by lowering levels of brain-derived neurotrophic factor (BDNF). Regular cannabis use during midlife has been associated with disruptions in white matter integrity, which can interfere with communication between different brain regions,” said Allder.
“Collectively, these structural and functional changes can undermine cognitive reserve and potentially accelerate age-related neurodegeneration,” he added.
Cannabis: Medical and recreational use increase in older adults
The study authors note that, in Canada, acute care for cannabis use in older people has increased since the liberalization of medicinal use in 2014, and the legalization of nonmedical use in 2018.
Medical use of cannabis products among older people is increasing, following anecdotal evidence that cannabis products may help some symptoms of dementia and other neurodegenerative diseases. However, there is no scientific evidence for this.
Edelmayer told MNT that only small clinical trials were being carried out to investigate this and it is, as yet, unknown whether any potential benefits might outweigh risks.
She emphasized the need for more research, including interventional, randomized studies to test the effects of these products.
“Importantly, the study suggests that severe cannabis use, rather than casual or moderate use, is linked to increased dementia risk. This reinforces concerns about rising cannabis use among older adults, especially as it’s increasingly used for both medical and recreational purposes.”
— Steve Allder, MD
View the original article on Medical News Today
