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September 15, 2021
High Minded: Neuroscientists Say THC Makes Us Dumber—So Why Does It Make Us Feel Smarter?

BY BEN THOMAS | Original illustration for Ember by Sebastian Konig

Cannabis enjoys widespread acclaim not only for its calming and pain-relieving effects, but also for brain benefits like enhanced creativity and an elevated sense of mental clarity. But while many users swear that cannabis improves their cognition, neuroscience research appears to indicate the opposite: THC measurably decreases performance on cognitive tasks—disrupting connectivity between brain regions, amplifying random neural “noise,” and creating much more confusion than clarity.

What’s leading so many scientists to these conclusions? Everyone who enjoys a productive high knows that cannabis can (and does) enhance awareness—so are all these researchers making some fundamental mistake(s)? Or are cannabis’s cognition-enhancing benefits really just placebo effects and illusions we experience because we want to experience them? 

Perhaps a bit of both, when we weigh all the facts. 

Let’s dig deeper into the neuroscience of cannabis cognition—and see why decades of scientific evidence seem to contradict so many people’s experiences.

The power of “weed insight”

Anybody who’s tried painting, brainstorming, or music-making on an uplifting sativa strain knows firsthand that cannabis can enhance creative focus, fuel productivity, and inspire innovative and out-of-the-box ideas. Many of us can remember struggling with a seemingly unsolvable problem, then taking a weed break and returning with fresh insight into the solution.

The power of “weed insight” has long been a major cannabis selling point. Jazz musician Louis Armstrong famously said the plant gave him “much better thoughts,” making him a more creative songwriter. Astrophysicist Carl Sagan credited it with broadening his empathy and sharpening his recall of childhood memories. Neurologist Oliver Sacks, meanwhile, said cannabis (along with psychedelics like LSD) “taught [him] what the mind is capable of.”

Today, many canna companies market sativa-based formulations with the promise that they provide exactly these kinds of mind-expanding benefits—which satisfied customers insist they do. One reviewer, for example, reports that a certain sativa tablet “keeps me feeling clear headed” and “100% socially alert,” while another happy customer reports, “[it] provides me with... mental alertness that helps me focus.”

In fact, the vast majority of cannabis advocates would agree that THC makes it easier to focus, stay alert, and think creatively. 

So why are hundreds of neuroscience studies finding just the opposite?

Perplexing results from neuroscience

Research on mind-altering chemicals typically takes a multi-pronged approach: studying their effects on brain function, as well as on people’s scores on attention and memory tasks—then looking for correlations between internal chemistry and external performance. This approach has taught us, for example, that caffeine speeds up brain activity through three different neurochemical pathways; and that these chemical shifts translate into faster reaction times, but reduce scores on long-term memory tests.

In a similar way, we might expect cannabis’s widely famed cognitive benefits to correlate with observably streamlined brain function. We might also expect people on THC to perform above average on alertness and focus tests. But surprisingly, evidence from neuroscience shows the exact opposite in both cases.

For example, a 2015 study led by Jose Cortes-Briones, a psychiatrist at the Yale University School of Medicine, found that delta-9-THC increases staticky “noise” and disorganized connectivity throughout the cerebral cortex—the largest, most highly developed brain layer. This seems to indicate that the brains of people on THC have to work harder to stay focused. 

What’s more, THC has yet to demonstrate any ability to enhance alertness or clarity in a controlled clinical environment. In fact, a 2013 study led by Matthijs Bossong, a neuroscientist at University Medical Center Utrecht, found that people on THC actually tend to perform below average on object-recognition and task-switching tests. 

Although these might sound like cherry-picked results, they line up with the findings of hundreds of other THC studies. In 2015, a team led by Michael Bloomfield, a clinical research fellow at University College London, conducted a systematic international review of more than 320 cannabis neuroscience papers—and found that nearly all agree THC makes it harder to focus, redirect attention, store and recall memories, and maintain a clear train of thought.

At first glance, these findings appear downright bizarre—as if hundreds of studies somehow concluded caffeine makes us sleepy instead of wakeful. Why would such a mountain of data indicate the opposite of what we’ve experienced? 

Maybe because we’re still missing some crucial pieces of the puzzle.

A picture still coming together

The startlingly poor performance of brains on THC might sound like a deathblow for the idea of cognition-boosting cannabis. Could it really be possible that “weed insight” is just a placebo effect—that Armstrong, Sagan, Sacks, and all those satisfied sativa reviewers felt inspired and alert simply because that’s what they wanted to feel?

High expectations (pun very intended) could certainly be one factor. Research also shows that creative insights tend to arrive when we take time away from the problem—and that new ideas often pop into our minds when we’re thinking about something seemingly unrelated. In other words, a weed break may help inspire insight simply by providing a change of scenery.

Still, there’s clearly more to this picture than just positive thinking and smoke breaks. So why are neuroscientists having such a hard time replicating insightful weed experiences? One reason could be their tunnel-vision focus on THC. Since scientists have no universal clinical standard for cannabinoid ratios, many researchers have opted for high-THC sativa extracts, or sometimes just chemically isolated delta-9-THC. This undoubtedly gives us an incomplete picture of cannabis’s neurological impact—since CBD, for example, offsets many of THC’s effects, sometimes even producing the opposite neural results of a “straight” THC dose.

And CBD is just one of the 144 (or more) different cannabinoids found in natural cannabis flower. All these compounds interact with one another—and with the body’s endocannabinoid system—in ways we’re only beginning to understand. So it’s entirely possible that future studies, using reasonable doses of full-spectrum cannabinoids, will yield results more in line with the cognition-enhancement experiences reported by so many cannabis enthusiasts. 

Even without such results, though, all these reports of weed-enhanced focus, alertness and clarity are still data points that demand explanation. If there’s no neurological basis for “weed insight,” then what’s the basis for the sensation of insight? In other words, if cannabis can’t really enhance cognition, then why does it so often feel as if it does?

These questions may not receive satisfying answers any time soon. But as a wider range of psychoactive compounds become available for research and clinical therapy, a more open-ended approach to investigation will likely lead to more of the insights we’ve been hoping for.


Ben Thomas is a journalist and novelist who's lived in 40+ countries. He specializes in telling stories from the frontiers of science, history, culture and the cosmos—and the points where all these fields intersect.

These statements have not been evaluated by the Food and Drug Administration. Products are not intended to diagnose, treat, cure, or prevent any disease.
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