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As the holiday season brings increased law enforcement patrols aimed at impaired drivers, the challenge of detecting cannabis impairment behind the wheel remains unsolved. Despite recreational cannabis being legal in several states for over a decade, police still lack a reliable method to determine whether someone has recently smoked or consumed cannabis and is too impaired to drive.
Researchers at the University of Colorado Boulder (CU Boulder) and the National Institute of Standards and Technology (NIST) are aiming to solve this issue. Their study, involving 45 regular cannabis users, is paving the way for developing a cannabis breathalyzer—one that could help establish standardized roadside testing protocols for impairment.
“The ultimate goal is to develop a reliable tool that supports fair law enforcement and helps keep our roads safe,” said Cinnamon Bidwell, associate professor of psychology and neuroscience and co-director of CUChange, a lab that studies the health risks and benefits of cannabis.
The Challenges of THC Detection
Unlike alcohol, which is exhaled in large quantities and easily measured in breath, cannabis presents a unique challenge. THC, the main psychoactive ingredient in cannabis, is exhaled in trace amounts, making it much harder to detect. Research by NIST shows that when alcohol is consumed, a single breath can expel a million times more ethanol than someone would exhale after consuming cannabis. This makes detecting cannabis intoxication akin to finding “a needle in a haystack,” according to Tara Lovestead, a NIST chemical engineer involved in the study.
Moreover, unlike alcohol, THC doesn’t have a clear correlation between the amount present in breath and the level of impairment, complicating the establishment of a “BAC equivalent” for cannabis.
A Mobile Lab to Map Cannabis Impairment
CU Boulder and NIST researchers are taking a novel approach with a mobile pharmacology laboratory—a white Sprinter van equipped with cutting-edge equipment. The van enables the team to measure the impact of legal cannabis products in real time, observing how THC levels in the breath change after consumption.
For the study, participants, aged 25 to 50, are divided into two groups. One group uses a THC-based flower strain, while the other uses a THC concentrate. Participants are given cannabis from Native Roots Dispensary in Boulder, ensuring consistency across the sample group.
After a baseline test, participants are free to consume cannabis and then return to the van for 13 additional breath tests over the following two hours. The team will analyze the over 1,200 unique samples to map how THC levels fluctuate with intoxication, providing crucial data that could inform future cannabis breathalyzers.
Testing the Multi-Breath Approach
Previous studies suggest that THC levels peak within 15 minutes of consumption and decline rapidly over the next few hours. The CU Boulder and NIST team hopes to confirm whether taking two breathalyzer tests—one shortly after consumption and another 10 to 20 minutes later—can reliably indicate recent use and impairment. If successful, this multi-breath approach could be key to accurately identifying cannabis impairment on the road.
A New Tool for Drivers and Law Enforcement
While the study doesn’t aim to develop its own cannabis breathalyzer, its findings could help inform the development of accurate, reliable tests for law enforcement use. The results could also benefit cannabis users, who may want a reliable tool to ensure they are not driving under the influence, whether for medical or recreational purposes.
“Most people who use cannabis, whether for recreational or medical reasons, want to do so responsibly,” Bidwell said. “If there is a tool they can use to assure they aren’t putting anyone at risk, that would be hugely beneficial.”
As the study continues, researchers hope to establish protocols that could one day lead to the development of a blood-alcohol-like threshold for cannabis, offering both law enforcement and cannabis users a reliable way to measure impairment.
