Cannabis May Protect Aging Brains—But There's a Catch, New Study Finds

A new study of over 26,000 middle-aged and older adults found that moderate cannabis use was associated with larger brain volumes and better cognitive performance, challenging long-held beliefs that the drug harms brain health in aging populations. The research, led by Dr. Anika Guha at the University of Colorado Anschutz Medical Campus, suggests that cannabis may have neuroprotective effects as we age—but only when used in moderation.

Why Are Older Adults Using Cannabis More Than Ever?

Cannabis use among older Americans is climbing rapidly. Nearly 1 in 5 people ages 50 to 64 reported using marijuana in the past year, along with 5.9% of those 65 and older. Unlike younger users, older adults are turning to cannabis primarily to manage chronic pain, sleep disorders, and anxiety—not for recreational purposes. This shift prompted researchers to ask an important question: what are the long-term effects of cannabis use as we continue to age?

"More older adults are using cannabis. It's more widely available and is being used for different reasons than in younger folks—such as for sleep and chronic pain," Dr. Guha explained. "Plus, people are living longer. We have to ask, 'What are the long-term effects of cannabis use as we continue to age?'"

What Did the Study Actually Find?

Researchers analyzed data from 26,362 adults ages 40 to 77, with an average age of 55, all living in the United Kingdom. Participants answered detailed questions about their cannabis use, underwent MRI scans to assess brain structure, and completed cognitive tests measuring learning, memory, processing speed, attention, and executive function.

The findings were striking. Older adults who used cannabis showed larger brain volumes in several regions, particularly in areas rich with cannabinoid receptors—the brain's natural docking stations for cannabis compounds. One key area was the hippocampus, which plays a critical role in memory and is closely linked to dementia risk. Cannabis users also performed better on cognitive tests across multiple measures.

The results were so consistent that even Dr. Guha was surprised. "I was a little surprised that every cognitive measure that demonstrated a significant effect showed better performance among cannabis users," she said. "It goes against your default assumptions, because I think a lot of research out there has shown cannabis is associated with worse cognitive function, at least acutely".

The Moderation Sweet Spot: When More Isn't Better

Here's where the story gets nuanced. The cognitive and brain volume benefits weren't consistent across all usage levels. For most brain regions and cognitive tests that showed an effect, moderate users had the largest brain volumes and best cognitive performance. Heavy users didn't show the same advantages—and in some cases, performed worse.

There were a few exceptions. In measures like right amygdala volume (a brain region involved in emotion) and visual memory and learning, heavy users actually posted the strongest results. This suggests dose-dependent effects—meaning the relationship between how much cannabis someone uses and the brain benefits isn't a simple straight line.

The research also identified one potential downside. Higher cannabis use was linked to lower volume in the posterior cingulate, a brain region involved in memory, learning, and emotional processing. However, Dr. Guha noted that some research suggests a smaller posterior cingulate volume is actually associated with better working memory, making the interpretation unclear.

What Makes Cannabis Potentially Protective for Aging Brains?

The exact mechanisms remain unclear, but researchers have some theories. Brain atrophy—the natural shrinking of brain tissue—is a hallmark of aging and is often correlated with reduced cognitive function and increased dementia risk. "It's not that bigger is always better," Dr. Guha explained. "But we also know that as we age, we often see smaller brain volumes due to processes like atrophy and neurodegeneration. That decrease is often correlated with reduced cognitive function and increased dementia risk".

Supporting evidence comes from other studies. A Danish study found that cannabis users experienced "significantly less cognitive decline" over their lifetimes than non-users. A U.S. study involving patients with HIV found that those with a history of occasional cannabis use showed stronger cognitive performance.

The key factors that may influence cannabis's effects on brain health include:

• Usage Pattern: How frequently and in what quantity someone uses cannabis appears to matter significantly, with moderate use showing the most consistent benefits
• Product Type: Different cannabis products (flower, edibles, oils) may have different effects on brain structure and function
• Reason for Use: Whether someone uses cannabis for pain management, sleep, anxiety, or recreation may influence outcomes
• Life Stage: The age at which someone begins using cannabis and how long they've used it may affect long-term brain health outcomes

What's Next for Cannabis and Brain Research?

Dr. Guha and her colleagues have another paper under review examining how cannabis affects brain function—not just brain structure—in the same group of older adults. "These data suggest there are also positive impacts of cannabis on the function of these brain regions, not just the size or volume of them, too," she said.

The researcher is also beginning to explore the link between brain health and psilocybin use, another once-taboo substance that has gone increasingly mainstream. "If people are using these substances, it's worth knowing what the impacts are, both good and bad," Dr. Guha noted.

In the United States, cannabis is legal in 40 of 50 states for medical use and 24 states for recreational use, making this research increasingly relevant to millions of older Americans considering cannabis for health reasons.

The bottom line: the story is nuanced. While moderate cannabis use appears linked to brain benefits in older adults, heavy use doesn't show the same advantages. Anyone considering cannabis for brain health or other reasons should consult with a healthcare provider, especially since individual responses vary based on genetics, overall health, and other factors.