Clinical Trial to Test Cannabis Impairment While Driving

Cannabis legalization came with several lingering fears about the effects this plant would have on society at large. One of the greatest fears has always been about the increase in cannabis-impaired vehicle crashes and fatalities.

Yet, nearly a decade into legal cannabis, measuring impairment continues to foil researchers and regulators. How do you determine whether a driver has recently consumed enough cannabis to impair their capacity to drive? More importantly, how do you do so without picking up traces of past cannabis use?

A new clinical trial working within an advanced driving simulation is set to start in 2021. This trial will explore the measurable effects of cannabis intoxication to develop brain-based biomarkers of impairment. The end goal is the creation of a new self-administered application to predict impairment before driving. However, from the start, the clinical trial seems to be missing some critical variables.

The Difficult Nature of Capturing Cannabis Impairment

As per "The Effect of Cannabis Compared With Alcohol on Driving," published in the American Journal of Addictions, there is evidence that cannabis intoxication does impair driving-related skills. Furthermore, just like alcohol, it does so in a "dose-related fashion." The problem? As per the authors of this review, "the effects between individuals vary more than they do with alcohol because of tolerance, differences in smoking technique, and different absorptions of THC." Two puffs on a joint create different intoxication levels among different people. Cannabis frustratingly doesn't follow the consistent and predictable impairment trajectory that alcohol consumption does.

To complicate matters further, cannabis may also linger in the body for more than a month following consumption. Metabolism, body mass index, gender, and consumption habits all influence exactly how long traces of THC exist in the human body. Roadside tests would need to capture impairment, but not historical use.

In a piece for CNN Business, David Randall Peterman, Congressional Research Service transportation analyst, described how "about two alcoholic drinks within an hour will cause a 160-pound male to experience a decline in visual functions and in the ability to perform two tasks at the same time." But, for cannabis? In his words, "Based on current knowledge and enforcement capabilities, it is not possible to articulate a similarly simple level or rate of marijuana consumption and a corresponding effect on driving ability." It's why there has been an alcohol breathalyzer since 1954, but as of 2020, there is no effective breathalyzer for cannabis.

National Advanced Driving Simulator at the University of Iowa Looks at Cannabis

In March 2021, the National Advanced Driving Simulator, located at the University of Iowa, is set to study cannabis impairment in partnership with Advanced Brain Monitoring Inc. (ABM Inc.). The clinical trial, launching with the federal government's approval, will put 75 cannabis users to the test to develop a Cannabis Impairment Detection Application (CIDA), which will help future cannabis users to predict their level of impairment.

As per the details listed on Good Clinical Practices Network, the two main goals of this driving simulation are as follows:

1. To better understand the effects of acute cannabis intoxication on driving performance in a driving simulator
2. To develop and refine brain-based biomarkers of impairment due to acute cannabis intoxication

Timothy Brown, the director of drug driving research at the University of Iowa, explained, "We want to know when someone is impaired so we can differentiate somebody who used cannabis two days ago, but it might show up on their system, versus somebody who used it an hour ago and is not safe to drive."

During the study, the participants will visit the driving simulator several times to complete a computerized task, followed by a 45-minute driving test. The test will measure the participant's blood pressure, heart rate, and where the eyes are focused, using electroencephalography and electrocardiography equipment.

Before each driving session, the participants will receive a cannabis dose, administered via the Volcano Vaporizer. As this is a federally approved study, both the placebo cannabis and the THC-rich cannabis come from the University of Mississippi facility (the only facility to supply all federal cannabis studies). The team plans to administer 0.5 grams of placebo cannabis (essentially hemp), high THC cannabis (7.5 percent), or very high cannabis (12.5 percent).

Advanced Driving Simulation Won't Tell the Full Story

The University of Iowa study plans to work with participants who have recreational experience with cannabis more than once a month but less than five times a week. Other than a physical exam and screening questions, there are no additional parameters on study participation.

The clinical trial already seems to neglect some key points. Will it look into age- and sex-related differences in impairment? Recent research has already demonstrated that both age and sex impact the effects and impairment of cannabis. They may also miss the differences of intoxication between new consumers and those who use cannabis daily. Tolerance to THC, which develops with frequent use, impacts the rate of intoxication and cognitive impairment.

Another dilemma? The quality of the cannabis the researchers are using in the clinical trial. Federally supplied cannabis is notoriously out of step with real-world products. In legal markets, cannabis with 7.5 to 12.5 percent THC is not considered "high" or "very highly" potent, unlike the categories given by the University of Mississippi's cultivation program.

In the real world, some strains naturally reach 30 percent THC. Consumers also love concentrates, which can reach levels of up to 99 percent purity. Not to mention the popularity of edibles, which the human body metabolizes into a significantly more potent metabolite than THC. How will these differences impact impairment while driving?

Neglecting to assess these essential pieces could impact the effectiveness of the final ABM Inc. app (can a mobile app effectively tell if the user is high?) It is a fair assessment that more in-depth research will be required to develop a genuinely predictive and reliable app. There is little research on how cannabis affects different demographics and almost no research on how demographic parameters influence driving impairment.

An app would need to work just as effectively for a young male with chronic cannabis habits as it would an older female who smokes infrequently. Thus far, it's unclear how this single driving simulation would result in the level of information needed to create these predictions.