“As the prevalence of cannabis use increases, the public perception of DUIC as safe and devoid of consequences is growing,” Metrik writes with co-author Dennis McCarthy, professor of psychology at the University of Missouri. “Shifting this perception and preventing DUIC will require clear messaging about risk, development of a consistent DUIC impairment standard and DUIC-specific statutes and law enforcement efforts.”
The authors describe the complexity of establishing a universally accepted method of testing for DUIC. Successful strategies against alcohol-impaired driving involve legal limits for blood alcohol concentration. Replicating a similar framework for cannabis poses challenges due to “differences in pharmacology and impairment indicators.” Metrik and McCarthy also suggest there aren’t enough police officers certified as Drug Recognition Experts (DREs) to identify drug-related impairment of drivers through psychophysical tests.
To overcome these obstacles, Metrik and McCarthy propose a comprehensive plan based on a “successful hurdles” approach: 1) an oral fluid test to detect recent cannabis use, followed by 2) behavioral assessment of impairment. They also emphasize the need for research that involves controlled studies with different levels of THC (the active ingredient in cannabis) and THC taken orally. This research is crucial for determining the right levels of THC corresponding to behavioral impairment that can be detected in oral fluid.
They also stress the importance of developing tools that can precisely recognize impairment. These would support DRE assessments and make it easier to evaluate behaviors. This is especially important for people using cannabis for medical reasons, who may have a higher tolerance to THC and thus may be less impaired. As a result, more sensitive assessments are needed beyond standard screening tests.
Finally, the researchers underscore the need to study the effectiveness of combining oral fluid testing with behavioral assessments, which is crucial to establishing consistent guidelines for determining impairment due to cannabis use while driving. Research on DUIC will also help clarify the risks of driving under the influence of cannabis, correct any misunderstandings in public perception, and help people make safer choices when driving.
“A better understanding of factors that influence people’s decision making to drive under the influence of cannabis is necessary to guide cannabis regulatory action on impaired driving,” said Metrik.
Metrik and McCarthy emphasize that this comprehensive approach will contribute to the development of a reliable DUIC impairment standard, which will inform policy and law-enforcement efforts.
