Cannabis Use and Executive Function

In pop culture, perhaps because cannabis is often placed in the same group as other recreational substances, stoners get a bad rap for being slow, under-performers. In the now-famous film Fast Times at Ridgemont High, one of the main characters, Jeff Spicoli, typifies the surfer/stoner as perceived by a large swath of society; he’s essentially an airhead. This type of media portrayal has given the population at large the idea that cannabis is not beneficial for long term mental health. To this degree, almost every medical cannabis user may experience the concern of a well-meaning friend who asks,

“That can’t be good for you over time, right?”

This is a good question for someone first exposed to any new medicine. Patients should be aware that even the most documented pharmaceutical medicines can be dangerous and misprescribed. As a result, everyone should be vigilant about the effect of taking a new medicine.

However, as we’ve covered in previous articles, we’re seeing no long-term irreversible effects statistically. The idea that cannabis is somehow destroying the machinery of the brain long-term is patently false. A more plausible argument might be that cannabis re-directs mental traffic. Sadly, anti-cannabis proponents have latched onto studies that give incomplete results. For instance, it may be true in one test that cannabis users on average perform more slowly. Researchers may then go on to find that when the same test population is weeded of heroin users, the negative effects disappear and all groups perform equally. In other words, readers should be careful to look for studies that control for associated variables or the data may be truly misleading.

Regardless, as medical cannabis expands from what is currently a 6-7 billion dollar industry, the mass effect on the population at large remains worth studying. A new paper from researchers at the Cognitive and Clinical Neuroimaging Core in Massachusetts has set out to determine the effect of cannabis use on executive functioning. “Executive functions”, for those unfamiliar, are major cognitive functions that facilitate decision-making and problem solving. To study this, the group collected 24 non-users of cannabis interested in using medical cannabis. Researchers defined “non-user” as somehow who had never consumed cannabis or had not consumed cannabis for ten years prior to the study (at ten years, there is no possibility that the level of cannabinoids remaining in patients could affect test results even remotely). Researchers confirmed purported use via drug-testing to ensure patients’ honesty.

At this point, researchers submitted patients to a battery of cognitive tests. The first test, the Stroop Color Word Test, “assesses the ability to inhibit an automatic, overlearned response.” Patients are asked to read the color of ink that various words are printed in, as quickly as possible in succession. Unfortunately, when these words are color names themselves, the natural human instinct is to say the word instead. Various parts of the test are designed to reinforce this tendency before testing. The second test, the Trail Making Test, “is comprised of two timed conditions where participants must connect a series of dots. Trails A measures psychomotor function, visual scanning, and attention by asking participants to connect dots in numerical order. Trails B incorporates alternating set demands, requiring participants to alternative between numbers and letters”, which is therefore measuring keeping track of two variables at the same time and switching between different tasks. Next, the Wisconsin Card Sorting Test (WCST) is a somewhat similar test in which patients match cards based on “sorting rules and adjust to changing sorting rules based solely on feedback as to whether each match is correct or incorrect”. In other words, this test establishes users’ abilities to draw and implement conclusions quickly. Finally, the Letter-Number Sequencing task requires patients to read strings of letters and numbers and repeat them accurately in order, before rearranging to say them again in alphabetical or numerical order.

Readers may notice that all of these tests revolve around using simple, well-known systems (numerical systems, letter systems) to tests how users are able to organize, remember, and process information. Additionally, to ensure that any changes in behavior being observed are due specifically to cannabis rather than behavioral or sleep changes, researchers performed quality of life, sleep, and general health questionnaires. Of the original 24 patients enrolled, 11 returned to repeat these tests after three months of medical cannabis treatment. Though amount and type of cannabis was self-chosen/administered, patients reported strain type and variety in an effort to provide researchers with further information. Patients reported an average cannabis use of 1.7 times/day and 9.3 episodes/week.

Strangely enough, not only did the final results indicate no decrease in cognitive performance, they actually indicated an increase! In the Trail Making Test, participants “completed Trails A significantly faster and also tended to complete Trails B faster relative to [their respective] baseline.” Likewise, “on the Stroop Color Word Test, participants also demonstrated faster completion times and some improvements in task accuracy” after three months of sustained cannabis use. On the other two tests, the Card Sorting test and the Letter Number Sequencing test, no significant results were observed in either direction.

How could this be? Does cannabis contain some sort of neurocognitive supercharging molecule? Juicy conclusion, but unlikely. The most likely cause is actually hinted by the quality of life and sleep testing results generated simultaneously in this study. Apparently, cannabis use allowed users to decrease opioid use and obtain better sleep, as well. Since opioids and other pharmaceuticals can yield a decrease in energy and cognitive function, being able to take less literally yields a cognitive improvement. Patients feel happier, more well-rested, and healthier. This should once again be no surprise to readers, as we’ve been harping for several years on the benefit of using cannabis to replace or at least partially decrease use of other pharmaceuticals. However, again, we’re now confronted with very real physical evidence that this substitution is worth patients’ time and will result in a quality of life increase.

The biggest drawback to this study, however, is not the rigor or planning but the limited sample number. What amounts to 11 returning users is a very, very small number of patients. While the results are indeed statistically significant and real, this therefore represents a weaker study than we’d hope to see in time. Ideally, future researchers will sample thousands of patients in one study. Unfortunately, due to limited manpower, time, finances, etc. obtaining a sample in the thousands is unusually difficult and requires national cooperation. As we enter the age of medical cannabis, however, the possibility of a large-scale study becomes more and more realistic. Readers may expect to see this type of study within the next decade.


Works Cited

Gruber SA, Sagar KA, Dahlgren MK, Racine MT, Smith RT and Lukas SE (2016) Splendor in the Grass? A Pilot Study Assessing the Impact of Medical Marijuana on Executive Function. Front. Pharmacol. 7:355. doi: 10.3389/fphar.2016.00355

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