The federal government is taking a new approach to testing for recent cannabis use, exploring a revised protocol for screening breath samples for THC. It’s the latest in an ongoing effort to find more reliable, accurate ways of field testing for marijuana impairment in drivers and others.
Researchers at the National Institute of Standards and Technology (NIST) and the University of Colorado say that taking two separate breath samples within an hour of one another might yield better results than just a single test does. The goal now is to see whether the approach can be translated into a usable field test.
“If their research is successful,” NIST said in a press release about the project, “it could lead to a roadside test for cannabis use that involves two breath tests given at a specified interval apart.”
For years, one of the more challenging problems around marijuana policy has been how to reliably test for very recent use that might still be impairing someone, for example a driver. Many common tests can show evidence of use in recent days or weeks, but current impairment is harder to detect.
“Currently, when police pull over a driver they suspect of cannabis impairment, they typically use a battery of roadside tests such as heel-to-toe walking or repeating a sentence correctly,” NIST said. “But field sobriety tests, as they are called, can be imprecise, weren’t designed for cannabis, and, according to a recent study, can lead to false positives.”
“This is potentially paradigm-changing,” NIST materials research engineer Kavita Jeerage said in a statement. “If successful, it could pave the way for on-the-spot detection of recent cannabis use by law enforcement.”
A single breath test hasn’t been shown to work conclusively for detecting drivers who use cannabis. Now, NIST is exploring another option: two breath tests separated by a specified time interval. Learn more about the new approach: https://t.co/l2BgR4ov39 pic.twitter.com/GkC00kGyDL
— National Institute of Standards and Technology (@NIST) August 15, 2024
NIST chemical engineer Tara Lovestead likened detecting THC in breath to “looking for a needle in a haystack” but emphasized the importance of better testing procedures.
“A reliable breath test for cannabis is both a public safety and equity issue,” Lovestead said in NIST’s news release.
Jeerage and Lovestead were among the authors of a study published last year that found that even when using carefully collected samples and laboratory analysis, THC levels in breath samples were too inconsistent to tell whether someone had smoked marijuana recently.
The pilot study using two breath tests is supports as part of a $1.5 million interagency agreement between NIST and the National Institute of Justice. Researchers plan to recruit about 45 people between the ages of 25 and 50 from the Denver and Boulder, Colorado, areas.
Half the participants will be assigned a THC-based strain of flower cannabis and half a THC-based cannabis concentrate. Due to federal rules that impede the ability of researchers to provide cannabis from dispensaries, study participants will need to purchase the products themselves and consume them in their own homes.
After consumption, participants will enter a mobile pharmacology laboratory parked near their homes. There, over two hours, they will complete 10 breath tests at set time intervals apart. Those breath samples will be analyzed for THC and its metabolites, as well as select other cannabinoids. Blood samples will also be taken, and participants will complete questionnaires on their cannabis use.
Separately, NIST has been involved in ongoing research to improve cannabinoid testing in marijuana and hemp samples—part of its Cannabis Laboratory Quality Assurance Program (CannaQAP) launched in 2020. Earlier this year, the group released a report on determining cannabinoid content in plant material samples, following earlier reports on moisture content and certain toxins and heavy metals.
Earlier this year, however, a Justice Department researcher expressed doubt over whether testing for the presence of cannabis in someone’s system was the right approach to guard against impaired driving.
A Justice Department research says states may need to “get away from that idea” that marijuana impairment can be tested based on the concentration of THC in a person’s system.
Frances Scott, a physical scientist at the National Institute of Justice NIJ Office of Investigative and Forensic Sciences, questioned the efficacy of setting “per se” THC limits for drivers that allow a person to be charged with driving while impaired based on the concentration of cannabis components in their system. Ultimately, there may not be a way to assess impairment from THC like we do for alcohol, she said.
“Maybe what we need to do is kind of get away from that idea that we can sort of have a number when it comes to marijuana and have that mean that you’re impaired,” Scott said. “And it may get into some different types of measures than we’re used to doing. So maybe it’s not a blood measure or a breath measure.”
Last summer, a congressional report for a Transportation, Housing and Urban Development, and Related Agencies (THUD) bill said that the House Appropriations Committee “continues to support the development of an objective standard to measure marijuana impairment and a related field sobriety test to ensure highway safety.”
Sen. John Hickenlooper (D-CO) sent a letter to the Department of Transportation (DOT) in 2022 seeking an update on that status of a federal report into research barriers that are inhibiting the development of a standardized test for marijuana impairment on the roads. The department was required to complete the report by November under a large-scale infrastructure bill that President Joe Biden signed, but it missed that deadline and published the report this April.
A study published in 2019 concluded that those who drive at the legal THC limit—which is typically between two to five nanograms of THC per milliliter of blood—were not statistically more likely to be involved in an accident compared to people who haven’t used marijuana.
Separately, the Congressional Research Service in 2019 determined that while “marijuana consumption can affect a person’s response times and motor performance … studies of the impact of marijuana consumption on a driver’s risk of being involved in a crash have produced conflicting results, with some studies finding little or no increased risk of a crash from marijuana usage.”
Another study from 2022 found that smoking CBD-rich marijuana had “no significant impact” on driving ability, despite the fact that all study participants exceeded the per se limit for THC in their blood.
Photo courtesy of Chris Wallis // Side Pocket Images.
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