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Abstract
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Key Points
- Driving under the influence of cannabis has been identified as a public health concern as medical and recreational cannabis availability increases in some countries.
- A recent randomized clinical trial found similar levels of acute driving impairment with THC-dominant cannabis and with a combination of THC-CBD equivalent cannabis using on-road driving tests that provided real-world conditions; however, CBD-dominant cannabis did not produce significant cognitive or psychomotor impairment compared with placebo in this trial.
- Media coverage of this study conveyed the findings as CBD-dominant cannabis not causing driving impairment while THC-dominant cannabis does, with the latter lasting up to 4 h post-dose.
- It is recommended that clinicians counsel about the risks of driving impairment when patients disclose use of cannabis products containing THC.
Driving under the influence of cannabis (DUIC) is an important public safety concern as access to medical and recreational cannabis increases in North America and internationally [1]. Following alcohol, cannabis is the most commonly detected drug in both crash-involved drivers and the general driving population [2, 3]. Medical and recreational use may differ in the cannabinoids used, however, which may differentially impact driving ability. ∆9-tetrahydrocannabinol (THC) is the most psychoactive cannabinoid and responsible for the intoxicating "high" and impairing side effects associated with cannabis. In contrast, cannabidiol (CBD) may counteract some THC effects but can still produce effects of drowsiness [4] which may impair one's driving ability. In addition to cannabinoid content, factors such as user tolerance, product potency, dosage, and route of administration affect the onset, intensity, and duration of impairment. It should also be considered that cannabis may affect driving performance acutely (in the short-term) or over the long-term if a person is using sufficient quantities of cannabis for a sustained period.
Although several studies have concluded there is moderate increased crash risk associated with acute cannabis use, few studies have explored the magnitude and duration of driving impairment with varying concentrations of THC and CBD including CBD alone [1, 5-7]. A randomized clinical trial (RCT) assessing cannabis use on driving performance by Arkell et al. drew significant attention on this subject recently as the first study to examine four experimental drug conditions: (1) CBD-dominant cannabis (13.75 mg CBD), (2) THC-dominant cannabis (13.75 mg ∆9-THC), (3) THC/CBD-equivalent cannabis (13.75 mg CBD; 13.75 mg ∆9-THC), and (4) placebo (trace CBD, ∆9-THC) [8]. This commentary aims to elaborate on its findings relative to past research and to provide context on how the available evidence can guide conversations on cannabis use safety and ultimately inform policymakers on public health implications.
An RCT to Examine Driving Impairment
The Arkell trial used a randomized, double-blind, within-subject, placebo-controlled, crossover design. Participants (n = 26 enrolled; n = 22 completers) received a unique vaporized cannabis dose during four sessions (1 drug condition per session, 1 week apart) and completed two on-road driving tests during each session - one at 40-100 min post-dose and one at 240-300 min post-dose. Participants were accompanied by a trained driving instructor who had dual accelerator and brake control access. Cognitive tests, biological specimen collection, and subjective drug assessments were administered at baseline and at subsequent intervals post-dose. The primary endpoint was standard deviation of lateral position (SDLP, a measure of horizontal lane weaving) at 40 and 240 min after cannabis consumption. At 40-100 min post-dose, SDLP was significantly increased after THC-dominant (2.33 cm, 95% CI, 0.08-3.86; p < 0.001) and THC/CBD-equivalent cannabis (2.83 cm, 95% CI, 1.28-4.39; p < 0.001) administration, but not after CBD-dominant cannabis (−0.05 cm, 95% CI, −1.49-1.39; p > 0.99), relative to placebo. At 240-300 min post-dose, all of the active doses were similar to placebo with no impairment detected...
Keywords: Cannabis impaired driving
Language: en |