A recent study provides insight into the acute effects of cannabis use on cognitive and psychomotor performance, particularly focusing on the differences between occasional and daily users. The findings indicate that daily users may develop a tolerance to some of the impairing effects of cannabis, while occasional users show more significant impairments in reaction time and memory tasks while high. The findings have been published in the Journal of Cannabis Research.
The researchers undertook this study due to the increasing relevance of cannabis impairment in public health, especially concerning motor vehicle crashes and workplace safety. Previous research has shown that cannabis can increase the risk of motor vehicle crashes, making it the second most frequently detected drug in fatally injured drivers in the United States. However, blood THC levels — the current standard for measuring impairment — have proven unreliable due to poor correlation with actual impairment and the potential for tolerance in regular users.
“I’m interested in cannabis impairment because the ability to develop tolerance to some effects of acute (very recent) use makes it a complicated topic to study,” explained study author Ashley Brooks-Russell, an associate professor at the Colorado School of Public Health at CU Anschutz.
“There is growing evidence that with daily use, particularly relatively heavy daily use, that people can develop tolerance to many of the effects. But we don’t know much about how quickly one can gain and lose tolerance, and to what extent tolerance is gained. For example, if cannabis affects reaction time, which would be very important for drivel safely, can someone gain tolerance to that effect to the extent they would not necessarily be unsafe to drive after using cannabis?”
The study recruited 86 healthy adults aged 25 to 45 between October 2018 and February 2020. Participants were divided into three groups based on their cannabis use: daily users (smoking or vaping cannabis at least once a day), occasional users (using cannabis one to two days per week), and non-users (no cannabis use in the month prior to the study). Key exclusion criteria included history of drug or alcohol dependence, obesity, color blindness, pregnancy, and shift work employment.
Participants used their own cannabis products, ensuring that the study reflected real-world usage patterns. The cannabis flower products were verified to contain 15-30% THC. Participants underwent a tablet-based assessment before and after smoking cannabis to evaluate reaction time, gap acceptance (decision-making), and working memory.
The researchers found that occasional users showed a slower reaction time after cannabis use. However, daily users did not exhibit significant changes, suggesting a tolerance to the effects of cannabis on reaction time.
When it came to gap acceptance, the ability to navigate through moving vertical lines, daily users took longer to complete the task post-cannabis use but improved their accuracy. This suggests a compensatory cautiousness, possibly indicating a prioritization of accuracy over speed.
The ability to accurately replicate shapes, an assessment of working memory, declined significantly among occasional users after cannabis use. They replicated fewer shapes accurately compared to their baseline performance. Daily users did not exhibit significant changes in their working memory performance post-cannabis use. This suggests that daily users may develop a tolerance to the memory-impairing effects of cannabis.
“The largest effects that we saw were in the area of short term memory,” Brooks-Russell told PsyPost. “I suppose I expected that we would see larger effects in reaction time, with people have slowed reaction time after cannabis use, but the more complex tasks of remembering and repeating shapes that had been displayed seemed to better differentiate the cannabis drug effect.”
The findings indicate that “there may be cognitive tasks/tests that could help identify if someone is unsafe to drive or unsafe to do something at work that could impact safety (e.g., use heavy machinery),” she explained.
Future studies could focus on more controlled dosing to better understand the relationship between THC levels and impairment. Exploring other cognitive and psychomotor tasks and extending assessments to different time points post-consumption could provide a more comprehensive understanding of cannabis impairment. Additionally, expanding the demographic scope beyond healthy adults to include older adults and those with different health conditions would enhance the generalizability of findings.
“We are hoping to develop objective tools that could be used by employers or law enforcement to better detect and distinguish impairment from cannabis, rather than just if someone regularly uses cannabis but may not be impaired,” Brooks-Russell said.
The study, “Effects of acute cannabis inhalation on reaction time, decision-making, and memory using a tablet-based application,” was authored by Ashley Brooks-Russell, Julia Wrobel, Tim Brown, L. Cinnamon Bidwell, George Sam Wang, Benjamin Steinhart, Gregory Dooley, and Michael J. Kosnett.
