February 11, 2025
By Ben Adlin
A federal agency this spring will convene government officials, forensics
experts, academics, industry representatives, law enforcement and
standards organizations for what it describes as “an open and candid
discussion” about “the path forward to realize meaningful cannabis
breathalyzer technology and implementation.”
The two-day event, hosted by the National Institute of Standards and
Technology (NIST), which is part of the U.S. Department of Commerce, is
scheduled to be held in Boulder, Colorado, on April 16 and 17.
According to a preliminary agenda sent to Marijuana Moment by a NIST
representative, topics to be discussed will include challenges facing
marijuana breathalyzer design and development, obstacles to prosecutors
handling drugged-driving cases and how NIST and others might partner to
advance the technology.
Findings of the workshop, “Building a Path Forward for Meaningful
Cannabis Breathalyzer Realization,” are set to be compiled into a NIST
internal report that the agency has said will be publicly available.
Further information about the event is forthcoming, the NIST representative
said.
Unlike with alcohol, there’s currently no widely accepted field test to
determine whether someone is under the influence of marijuana.
In 2023, a federally funded report by researchers at NIST and the
University of Colorado Boulder concluded that evidence does “not support
the idea that detecting THC in breath as a single measurement could
reliably indicate recent cannabis use.”
“A lot more research is needed to show that a cannabis breathalyzer can
produce useful results,” Kavita Jeerage, a NIST materials research
engineer and co-author of the report, said at the time. “A breathalyzer test
can have a huge impact on a person’s life, so people should have
confidence that the results are accurate.”
More recently, a U.S. Department of Justice researcher cast doubt on
whether a person’s THC levels are even a reliable indicator of impairment.
States may need to “get away from that idea,” Frances Scott, a physical
scientist at the National Institute of Justice (NIJ) Office of Investigative and
Forensic Sciences under DOJ, said on a podcast early last year.
Scott questioned the efficacy of setting “per se” THC limits for driving that
some states have enacted, making it so a person can 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.
One complication is that “if you have chronic users versus infrequent users,
they have very different concentrations correlated to different effects,” Scott
said. “So the same effect level, if you will, will be correlated with a very
different concentration of THC in the blood of a chronic user versus an
infrequent user.”
That issue was also examined in a federally funded study last year that
identified two different methods of more accurately testing for recent THC
use that accounts for the fact that metabolites of the cannabinoid can stay
present in a person’s system for weeks or months after consumption.
Last October, a study preprint posted on The Lancet by an eight-author
team representing Canada’s Centre for Addiction and Mental Health,
Health Canada and Thomas Jefferson University in Philadelphia identified
and assessed a dozen peer-reviewed studies measuring “the strength of
the linear relationship between driving outcomes and blood THC” published
through September 2023.
“The consensus is that there is no linear relationship of blood THC to
driving,” the paper concluded. “This is surprising given that blood THC is
used to detect cannabis-impaired driving.”
Most states where cannabis is legal measure THC intoxication by whether
or not someone’s blood THC levels are below a certain cutoff. The study’s
findings suggest that relying on blood levels alone may not accurately
reflect whether someone’s driving is impaired.
“Of the 12 papers included in the present review,” authors wrote, “ten found
no correlation between blood THC and any measure of driving, including
[standard deviation of lateral position (SDLP)], speed, car following,
reaction time, or overall driving performance. The two papers that did find a
significant association were from the same study and found significant
relationship with blood THC and SDLP, speed and following distance.”
Earlier last year, researchers behind a federally funded study said they’d
developed new procedures to enhance the selectivity of a popular forensic
testing method, allowing better detection of delta-9 THC and its metabolites
in blood.
A 2023 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.”
A year earlier Sen. John Hickenlooper (D) of Colorado sent a letter to the
Department of Transportation (DOT) 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 under a large-scale infrastructure bill
that President Joe Biden signed, but it missed its reporting deadline.
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.
Evan as far back as 2015, a U.S. National Highway Traffic Safety
Administration (NHTSA) concluded that it’s “difficult to establish a
relationship between a person’s THC blood or plasma concentration and
performance impairing effects,” adding that “it is inadvisable to try and
predict effects based on blood THC concentrations alone.”
In a separate report last year, NHTSA said there’s “relatively little research”
backing the idea that THC concentration in the blood can be used to
determine impairment, again calling into question laws in several states
that set “per se” limits for cannabinoid metabolites.
“Several states have determined legal per se definitions of cannabis
impairment, but relatively little research supports their relationship to crash
risk,” that report said. “Unlike the research consensus that establishes a
clear correlation between [blood alcohol content] and crash risk, drug
concentration in blood does not correlate to driving impairment.”
Comments