Cannabis use causes memory problems, and they may be permanent

A new study has revealed how both recent and lifetime cannabis use can affect cognitive function. In particular, cannabis use was linked to reduced neural activity during working memory tasks. 

The project – among the largest to investigate cannabis and cognition – examined more than 1,000 adults aged 22 to 36, using cutting-edge brain imaging techniques to assess the impact of cannabis on various mental processes.

Cannabis and working memory 

The research team discovered that 63% of heavy lifetime cannabis users showed diminished brain activation in key regions while performing a working memory exercise, while 68% of recent users demonstrated a similar pattern. 

Working memory, a cognitive ability essential for temporarily storing and manipulating information, underpins a wide array of everyday tasks, such as following directions or solving mental calculations.

Joshua Gowin is the study’s first author and an assistant professor of radiology at the University of Colorado School of Medicine. 

“As cannabis use continues to grow globally, studying its effects on human health has become increasingly important,” Gowin explained.

“By doing so, we can provide a well-rounded understanding of both the benefits and risks of cannabis use, empowering people to make informed decisions and fully comprehend the potential consequences.”

Distinguishing cannabis users by intake

The researchers classified study participants into three groups, based on cannabis usage history:

• Heavy users: Over 1,000 total instances of cannabis use
• Moderate users: Between 10 and 999 total uses
• Non-users: Fewer than 10 total uses

The volunteers completed seven cognitive tasks – ranging from working memory and reward assessment to emotional processing and language skills – while undergoing functional magnetic resonance imaging (fMRI). 

This approach allowed scientists to examine real-time brain activity in response to different stimuli.

Working memory: The most vulnerable function

While many of the tasks revealed subtle cognitive differences, the most pronounced effect appeared in working memory.

“We applied the highest standards to our research, setting rigorous thresholds for statistical significance across all seven cognitive function tests. To minimize the risk of false positives, we employed false discovery rate (FDR) correction,” noted Gowin. 

“While some of the other tasks indicated potential cognitive impairment, only the working memory task showed a statistically significant impact.”

Reduced working memory performance manifested in lower neural activation within regions such as the dorsolateral prefrontal cortex (DLPFC), dorsomedial prefrontal cortex (DMPFC), and the anterior insula.

These areas are closely tied to decision-making, problem-solving, and the integration of thoughts and emotions.

Cannabis use and brain function 

Notably, the researchers found that refraining from cannabis prior to cognitive testing might offer some improvement in working memory performance.

However, abrupt cessation could also temporarily disturb cognitive function, especially among heavy users, due to potential withdrawal symptoms.

“People need to be aware of their relationship with cannabis since abstaining cold turkey could disrupt their cognition as well. For example, heavy users may need to be more cautious,” said Gowin.

This dynamic highlights the complexity of cannabis’s impact on cognition, emphasizing that moderation or gradual reduction may be preferable for individuals wishing to protect or recover working memory capabilities.

Further research is needed 

While the findings confirm a clear correlation between cannabis use and reduced working memory function, the researchers emphasize there is still much to learn about how these effects might vary across age groups, usage patterns, and individual physiology.

“There are a lot of questions we still need answers to regarding how cannabis impacts the brain. Large, long-term studies are needed next to understand whether cannabis use directly changes brain function, how long these effects last and the impact on different age groups,” noted Gowin.

Such extended research could clarify the duration of these cognitive impacts, determine whether they persist long after cessation, and identify any unique vulnerabilities among younger or older populations.

Understanding the risks and benefits 

As cannabis use gains broader acceptance and legalization in many regions, these findings bear considerable weight on both public health strategies and policy considerations. 

By highlighting potential risks to memory and daily functioning, this research serves as a reminder of the importance of understanding both the benefits and drawbacks of cannabis consumption.

Ultimately, knowledge gained from such studies could shape guidelines and interventions, aiding individuals and communities in making well-informed decisions about cannabis use – particularly in contexts demanding a high degree of working memory and cognitive performance.

The study is published in the journal JAMA Network Open.

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