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- Heavy cannabis users showed less brain activity in areas related to memory and thinking skills.
- Brain differences were still there even when recent cannabis use was considered, suggesting lasting effects.
- Recent users didn’t do as well on memory and verbal recall tests even when not high.
- Cannabis affected men’s brain areas for movement more than women’s in recent use cases.
- How often cannabis was used over a lifetime was a better sign of brain changes than being diagnosed with dependence.
As cannabis use becomes more accepted worldwide, researchers are working hard to learn how it really affects thinking, especially memory. A study in JAMA Network Open adds to proof that cannabis can change brain activity, mainly during memory tasks, and some effects last after the high is gone. This article explains what we know about cannabis and memory, the details of memory loss from weed, and what it means for people who use it for fun or medicine.
Cannabis and the Brain: The Basics
Cannabis affects the brain mostly through THC, its main ingredient that causes the high. THC works with the body’s endocannabinoid system (ECS), which is important for controlling mood, memory, sleep, and hunger. THC connects to cannabinoid receptors—especially CB1 receptors—which are found a lot in brain areas for memory, such as:
- The hippocampus (for making and getting back memories)
- The prefrontal cortex (for decisions and working memory)
- The cerebellum and basal ganglia (important for movement control and coordination)
When THC connects to these receptors, it changes normal brain signals. This causes the happy “high” but also affects short-term memory and other thinking skills. These effects have been known for a long time, but better brain scans are showing more about what happens to the brain’s structure and function from cannabis use over time.
Weed and Memory: What the Data Show
One of the most common findings in cannabis research is what it does to short-term memory. Cannabis has often been shown to make it harder to learn and recall new information. But does this cause lasting harm? Or do the effects go away when the drug is out of your system?
A big report from the National Academies of Sciences, Engineering, and Medicine in 2017 said that cannabis hurts memory when someone is high, mainly short-term and working memory. But, proof about long-term effects was not clear—until more recent brain scan research started to show more.
The JAMA Study: Looking at Cannabis Brain Activity
In a very detailed recent study, researchers looked at people from the Human Connectome Project. This huge set of data has thousands of brain scans and details about thinking tests. The 2024 study split people into three groups based on how much cannabis they used in their lives:
- Nonusers: 10 or fewer uses in their life
- Moderate users: Between 11 and 999 uses
- Heavy users: 1,000 or more uses
Using fMRI, researchers measured activity in certain brain areas while people did tasks that needed memory, emotion recognition, language, and movement control.
Memory Task: Where Differences Show Up
The main finding was in the working memory task, which asks people to hold and use information briefly—like to a list of letters or numbers. fMRI scans showed that heavy cannabis users had much less activity in these areas:
- Dorsolateral Prefrontal Cortex (DLPFC): Important for working memory and focus
- Medial Prefrontal Cortex (mPFC): Helps control decisions and thinking about yourself
- Anterior Insula: Plays a part in awareness and emotion control
These areas are key for handling tasks, emotions, and social behavior. Less activity here suggests that the brain may need to work harder—or not work as well—during tasks that need thinking.
Not Just About Being High
What makes these findings strong is that they considered recent cannabis use. Urine tests were done to remove people who had used cannabis recently (usually in the past one to four weeks, depending on how much they used). Importantly, even past heavy users who had not used cannabis recently still showed less brain activity in memory areas.
This points to a longer-term or maybe lasting change in how the brain works during memory tasks—which questions the common idea that all cannabis-related thinking problems disappear quickly after stopping use.
Cannabis and Cognitive Performance
While brain scans showed less activity, thinking performance is more complex. Here’s what researchers found:
- Recent users did worse on working memory and verbal memory tests—even when not high at the time.
- Heavy lifetime users did not always do worse, but they were less efficient at finishing tasks (suggesting their brain was working harder).
- Less brain activity during memory tasks was related to lower overall intelligence and verbal ability scores.
These findings suggest that while users might be able to make up for it in how they act for a while, the brain needs more effort—or uses different ways—to keep up performance over time.
Weed Memory Loss vs. Dependence
A surprising part of the study was that **cannabis use disorder (CUD)**—a diagnosis of problem cannabis use—did not strongly show brain activity changes. Instead, how often someone used it over their life was a more important sign. In other words:
You don’t have to be addicted for cannabis to affect your brain.
This is important for judging risk in health care. Doctors usually look for signs of dependence to see thinking risks, but this study says a wider view is needed.
Cannabis, Emotion, and Social Cognition
Your brain does more than just things; it also helps you in social situations. The study looked at theory of mind, or knowing what others are thinking or feeling. Doing poorly on these tasks was linked to recent cannabis use, showing a possible short-term problem in social understanding and feeling empathy. But, fMRI data did not always show activity changes in these tasks, so more study is needed.
Still, it is important: even just using cannabis sometimes might slightly affect your ability to read emotions or act right in social situations—a key part of mental health and relationships.
Sex Differences: Does Weed Affect Men and Women Differently?
A more and more important topic in cannabis research is gender or sex-based brain differences. The study saw that male recent cannabis users showed less brain activity during movement tasks, while female users did not. Even though it was just in one task, this pattern relates to bigger talks about how sex hormones, body processes, and stress might change cannabis brain activity.
Other studies have backed up these early findings, noting that women may be more sensitive to some high effects but also maybe stronger against long-term structure changes. More long-term studies that focus on sex differences are needed to make firm ideas.
Memory, Brain Efficiency, and Neuroplasticity
One idea from this and similar studies is brain efficiency. That is:
Your brain may do the same work but with more effort—or using different brain pathways—if affected by long-term cannabis use.
This idea is similar to other research on brain disorders, where the brain’s ability to change lets people learn ways to cope even when some areas get worse. For cannabis users, this could mean memory problems may take time to show, especially when stressed, aging, or doing many things at once.
Clinical and Public Health Implications
These results are important for a few groups:
- Young adults whose brains are still growing could have stronger or longer-lasting effects, especially with regular use or high-THC use.
- Medical cannabis users might want to think about dose, type (CBD vs. THC-heavy types), and how often to use to lower harm to memory.
- Teachers and parents should know that even if cannabis use is not a problem, it might affect learning.
- Lawmakers and health groups should support research that tells the difference between safe, moderate use and use that might hurt thinking skills.
A key point is that being informed, moderate, and careful about use is important. Just because cannabis is legal—or even helpful—does not mean it has no effect on thinking.
Questions for Future Study
The research brings up many new questions:
- Do memory-related cannabis effects go away if someone stops using it for a long time?
- Do genes and family history change how likely someone is to have memory problems?
- How does using cannabis early in life affect brain function later in life?
- Can some cannabinoids (like CBD) lessen the bad effects of THC-heavy types?
Studies over time and experiments are very needed to answer these questions and give advice for different types of cannabis users.
Tips for Cannabis Users Concerned About Memory
If you use cannabis now and worry about its effects on memory or thinking, think about these:
- Find out your thinking baseline—through therapists or online brain training sites.
- Use it less often or use less strong types if memory problems start.
- Do things that protect the brain like mindfulness, exercise, and good sleep.
- Think about types with more CBD, which may be less harmful and even brain-protecting based on early proof.
- Take breaks from use, letting the brain rest to reset thinking pathways.
Knowing is power—and knowing the real link between cannabis and memory lets users make better choices without fear or shame.
References
- Gowin, J. L., Ellingson, J. M., Karoly, H. C., Manza, P., Ross, J. M., Sloan, M. E., Tanabe, J. L., & Volkow, N. D. (2024). Brain Function Results of Recent and Lifetime Cannabis Use. JAMA Network Open, 7(4), eXXXXXX. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2829657
- Volkow, N. D., Baler, R. D., Compton, W. M., & Weiss, S. R. B. (2014). Bad Health Effects of Marijuana Use. New England Journal of Medicine, 370(23), 2219–2227. https://doi.org/10.1056/NEJMra1402309
