Is Marijuana Safe for Your Brain?

What about the effects on your brain health? The truth is there’s a lot we don't know about marijuana and cognition in older adults. “To my knowledge, there are very few studies on older adults,” Haney says. One reason is that, on a federal level, marijuana is still classified as a Schedule I controlled substance, meaning it’s the most strictly regulated; this makes studies difficult to do, Haney explains.

The limited research we do have on older adults has been a mixed bag. One study of 19,932 adults with a mean age of 68, published in Age and Ageing in 2024, compared the brain scans of cannabis users to those who never partook. The researchers found that cannabis users had lower total brain volumes and less gray and white matter than abstainers, and that long-term users had the most brain atrophy. 

However, 1,457 of the participants received a second brain scan around two years later, and when the researchers compared the earlier MRIs to the later ones, they found no difference in the rate of brain aging between marijuana users and non-users. 

“Overall, we demonstrate seemingly inconsistent results,” the researchers note. Like Haney, they point out that “studies among older adults are scarce” and conclude that “further investigation of the consequences of cannabis use to brain health in late life is warranted.”

In 2022, based on the available evidence, the American Heart Association issued a scientific statement about marijuana that expressed “concerns about its potential long-term effects on cognitive function.”

Your health care provider can help you consider the risks, but only about half of older adults who use cannabis regularly have talked to their doctors about it, according to the National Poll on Healthy Aging. That’s concerning, Haney says, particularly because “cannabis can affect how you metabolize other medications.” An estimated 89 percent of adults age 65 or older take at least one prescription drug, and half of them report taking four or more. For this reason, it’s important to raise the issue with your doctor, Haney stresses.

Edibles, such as gummies, have an additional downside: They can be unpredictable. Because they go through your digestive system, they take longer to start working — anywhere from 30 minutes to two hours — and can last in your system up to 12 hours. That means the effects can come on suddenly and unexpectedly — like feeling off-balance, for example, which can increase your risk of a fall. Despite these drawbacks, gummies for sleep are popular — but do they work? Haney says that while they might be used occasionally, they can ultimately disrupt your sleep cycles and are “not a good long-term solution.” 

The bottom line: “Cannabis is not a totally benign wellness product — it’s a drug,” Haney says. “It’s not all good or all bad, but understand that there are risks.”