By Jenny Menzel, H.C.
With the legalization of marijuana for medicinal and recreational use in many states, people’s ability to drive safely while under the influence has been high on the list of concerns. In fact, an ecological study published by JAMA Internal Medicine revealed that upon the passing of recreational cannabis laws (RCLs), Colorado saw an increase of 75 traffic fatalities within that year.
But fast forward six months later, and another JAMA study dug a little deeper to determine whether cannabis and its constituents can impair driving performance. This time, researchers took a specific look at whether the two most common cannabinoids, tetrahydrocannabinol (THC) and cannabidiol (CBD), might cause decreased driving ability on their own or together.
The Study Demographics
Beginning May 2019, a nine-month double-blind, randomized clinical trial conducted at the Faculty of Psychology and Neuroscience at Maastricht University in the Netherlands monitored the driving skills of 26 healthy cannabis consumers — 10 men and 16 women, roughly between the ages of 20 to 26.
Before the driving tests, participants were given varied combinations of vaporized cannabis or a placebo. These combinations included:
- THC-dominant cannabis
- CBD-dominant cannabis
- THC/CBD equal combination cannabis
Upon inhalation of approximately 13.75 mg doses of cannabis or the consumption of a placebo, study subjects drove 62 miles in an on-road driving test using the standard deviation of lateral position (SDLP), a test measuring levels of swerving, overcorrection, or weaving between lanes.
85% of participants completed all eight driving tests administered throughout the study, with two tests commencing at 40 minutes and 240 minutes, respectively, after dosing within one testing day.
So what did these tests reveal?
The Study Results
Forty minutes after inhaling cannabis vapors or receiving placebos, SDLP testing determined participants given CBD-dominant cannabis scored the best (lowest) on the driving test — a hair lower than even the placebo group. Drivers given THC-dominant cannabis or an equal combination of THC/CBD scored higher, between 20-21 cm, showing more swerving during the driving test. While the increase in scores of those using cannabis with THC in it seems slight, the difference is especially evident when compared with the second driving test.
Administered at 240 minutes post-consumption, a second driving test showed SDLP in CBD-dominant cannabis users and placebo groups remained relatively the same, while those who were given cannabis with THC experienced fewer driving inaccuracies. Still, even after four hours, groups given THC-dominant cannabis swerved and overcorrected noticeably more than participants who were given only CBD or a placebo.
When compared to the placebo, test subjects given CBD-dominant cannabis measured relatively equal, and even slightly better, on two different driving tests. This suggests those that took the placebo or CBD performed better, swerving and overcorrecting significantly less than the drivers given THC-dominant cannabis or a 50/50 THC/CBD combination.
It’s important to note that participants were only occasional cannabis consumers, and the doses given to test subjects may not accurately represent the common recreational usage in some people. According to this study, however, research indicated that CBD-dominant cannabis didn’t impair driving performance. But dosage, tolerance, and potential side effects need to be taken into account as an important variable warranting further research to support these findings.
- Arkell TR, Vinckenbosch F, Kevin RC, Theunissen EL, McGregor IS, Ramaekers JG. Effect of Cannabidiol and Δ9-Tetrahydrocannabinol on Driving Performance: A Randomized Clinical Trial. JAMA. 2020;324(21):2177–2186. doi:10.1001/jama.2020.21218
- Santaella-Tenorio J, Wheeler-Martin K, DiMaggio CJ, et al. Association of Recreational Cannabis Laws in Colorado and Washington State With Changes in Traffic Fatalities, 2005-2017. JAMA Intern Med. 2020;180(8):1061–1068. doi:10.1001/jamainternmed.2020.1757
Jenny Menzel, H.C., is a Certified Health Coach and branding specialist for various alternative healthcare practices, and volunteers her design skills to the annual grassroots campaign, the Lyme Disease Challenge. Jenny was diagnosed with Lyme in 2010 after 8 years of undiagnosed chronic pain and fatigue, and continues to improve by employing multiple alternative therapies, including Āyurveda, Chinese Medicine and Bee Venom Therapy.