Despite setbacks in 2024 – losing the three state ballots it appeared on – cannabis legalization marches on. Recreational cannabis remains legal in 24 states. While 41 states have approved it for medical use.
And it’s big business. Sales topped out at $2.6 billion in 2023 (the most recent full year for which data is available). While they’re still crunching the numbers, analysts expect 2024 sales to have jumped more than 9 percent. So it’s not surprising that the science has been fighting to catch up to the economics.
Despite evidence that hints at a link between widespread accessibility and higher usage rates, public perception still (overwhelmingly) sees cannabis as a harmless – if not beneficial – drug.
Previous studies have also exposed:
- A rise in the prevalence of cannabis use disorder.
- Higher rates of cannabis-related motor vehicle crashes.
- Increased health risks, such as hyperemesis syndrome and cardiovascular disease.
Cannabis Concerns Drives Research
But researchers like Joshua Gowin, PhD, assistant professor of radiology at the University of Colorado School of Medicine, couldn’t help but notice a dearth of research on “the effects of cannabis use on brain function across multiple domains.”
“As cannabis use continues to grow globally, studying its effects on human health has become increasingly important,” Godwin, who’s also the study’s first author, said in a press release. “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.”
So Godwin and his team launched the largest study to date to figure out the long-term effects of the drug on brain function and cognitive performance.
The study – based on data pulled from the Human Connectome Project (HCP) – unearthed some notable findings on how lifetime (and recent) cannabis use shapes brain activity and cognitive functions, such as memory and social processing.
The researchers found that nearly two-thirds – 63 percent – of heavy lifetime users showed reduced brain activity during a working memory task. The more recent users performed only slightly worse, with 68 percent of them exhibiting the same memory struggles.
The team defined “heavy users” as those who’ve used cannabis more than 1,000 times over their lifetime. (Keep in mind that all of the study participants were between 22 and 36 years old.) “Moderate users” admitted to consuming it anywhere from 10 to 999 times.
The Brain Regions Cannabis Attacks
The CU scientists looked at the brain function in participants who engaged in seven distinct cognitive tasks, while accounting for lifetime cannabis use, recent use confirmed through toxicology screenings, and other demographic factors.
The researchers found a link between heavy lifetime cannabis use and lower brain activation, especially during working memory tasks. The lower brain activation they discovered showed up most prominently in the dorsolateral and dorsomedial prefrontal cortex and the anterior insula, known for their high cannabinoid receptor density. The diminished brain activation persisted even after excluding individuals with recent cannabis use, suggesting that long-term neural adaptations might be taking place alongside heavy exposure.
These results, the authors add, line up with previous data that suggests that THC, the psychoactive component of cannabis, can reduce the density and sensitivity of cannabinoid receptors in these brain regions.
What About Cognitive Performance?
Brain activation levels during working memory tasks appear to be linked to cognitive indicators – such as verbal episodic memory, intelligence, and education. Lower brain activation during both working memory and motor tasks at first seemed related to recent cannabis use. But these results failed to hold up after statistical corrections, suggesting that recent exposure might have more temporary effects.
One crucial implication of the findings is the importance of abstaining from cannabis use before engaging in cognitively demanding activities. Earlier research indicated that residual cognitive effects might linger for as long as four weeks after cessation.
The study also uncovered sex-related differences in brain activation during motor tasks. Men revealed lower activation when they tested positive for THC, while women didn’t. The researchers emphasized the need for more studies examining sex-specific effects of cannabis throughout the lifespan.
In addition to working memory, the research highlighted diminished brain activation during social cognitive tasks related to theory of mind. This supports earlier data that linked cannabis use to impairments in social processing.
Next Steps
As legalization continues to spread, understanding what the drug does to brain function is crucial for better-informed health policies and user awareness. This study is an important step toward clearing up how exposure influences neural processing and cognitive performance. But, Gowin adds that their study also shows that abstaining before tackling cognitive tasks could help.
“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,” Gowin said. “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.”
Further Reading
FDA Approves Cannabis Study for Veterans with PTSD
