Current Roadside Tests For Marijuana Impairment Are ‘Pseudoscientific,’ Law Professor Says

Roadside tests for marijuana impairment that are widely used by police
departments across the U.S. are “inadequate,” according to a newly
published commentary by a Rutgers University law professor who is urging
policymakers to take a more scientifically robust approach to
transportation safety while relying less on law enforcement’s ostensible
expertise.

The paper, by William J. McNichol of Rutgers University’s Camden School of
Law, asserts that current approaches to detecting cannabis impairment
“either merely imitate tools used to identify alcohol based impairment
without taking into account important differences between the effects of
these molecules or they are pseudoscientific ‘police science.'”

“The substance-use science community must take the lead in formulating an
informed marijuana impairment detection policy,” McNichol writes, “rather
than leave this in the hands of law enforcement.”

As more jurisdictions legalize and regulate marijuana, the paper says,
minimizing potential harm “depends on being able to promptly, accurately,
and objectively identify dangerous, marijuana- based impairment on the
highway and in the workplace,” McNichol argues. “Existing tools for making
this on-the-spot, medico-legal determination are inadequate, owing in large
part to their lack of scientific rigor.”

Unlike what he describes as a scientifically validated “close correlation”
between blood alcohol concentration and fatal vehicle accidents, tests for
the presence cannabinoids and their metabolites don’t provide a clear
indication that someone is behaviorally impaired.

“The science is fairly clear that the presence per se of cannabinoids in
bodily fluids ‘provides little, if any, information concerning behavioral
impairment,'” the article says, citing past research.

“Even if there was a well-demonstrated correlation between impairment and a
specific concentration of cannabinoids in bodily fluids,” it adds, “the
analytical chemistry required to reliably quantify cannabinoids in body
fluids is difficult to execute in the field. Police departments have been
reported to have given up on it, even after expending significant resources
on the attempt.”

Another approach to identifying impairment is the use of so-called drug
recognition experts (DREs) or workplace impairment recognition experts
(WIREs).

“Both DREs and WIREs claim that their expert opinions on the question of
impairment are objective, reliable, and grounded in science,” McNichol
writes, “even though the procedures they use were never designed to detect
impairment and do not do so.”

The use of DREs, which originated at the Los Angeles Police Department, “is
very popular among police officers and prosecutors,” he notes:

“It is a classic example of ‘police science’—techniques developed by police
officers for use in their police work. That is to say, it is not
science-based at all but is merely a police officer’s lay opinion encrusted
with some of the trappings but little or none of the substance of science.”

For example, DRE protocols typically call for investigators to check to see
whether a subject’s muscles feel “normal,” “rigid” or “flaccid,” the paper
says, even though health care professionals “do not measure muscle tone
this way…and would not recognize a police officer’s roadside squeezes as a
valid method of measuring muscle tone.”

Other signs of impairment, according to DRE training, include a high heart
rate and elevated blood pressure, McNichol points out, “even though about
half of the U.S. adult population has high blood pressure when completely
sober…to say nothing of the effect on one’s blood pressure of having a
police officer measure it on the roadside or in a police station after an
accident—settings that in 2009 the Kentucky Supreme Court recognized can
fully account for elevated blood pressure.”

“The lack of scientific rigor in the DRE Protocol,” the paper says,
“inevitably leads to inconsistent, almost random results.”

“In a 1998 controlled lab study,” it adds, “the DRE Protocol produced
either false negative or false positive results 45.5% of the time—not much
better than a coin toss.”

The solution to the problem, McNichol suggests, is simple—though not
necessarily easy to achieve.

“We must actually do what, so far, we have only pretended to do,” he
writes. “We must develop and adopt a scientifically valid, objective, and
reliable method for detection of marijuana-based impairment that can be
practically implemented in the field.”

A law professor, McNichol does not dig deep into alternative roadside tests
for cannabis use, but he calls for the development of “new psychomotor
tests” as well as further study into potential “biochemical markers of
impairment—including the full range of natural and synthetic cannabinoids
as well as their metabolites.”

“Most importantly, leadership of the legal and public policy discussions in
this area must not be left in the hands of police officers and their
associations, as is now the case,” he writes. “The substance-use science
community must take the lead, not only in the basic research that provides
the foundation for sound laws and policies but also in the legal and policy
discussions that will establish those sound policies.”

The new editorial from McNichol, initially published online late last year,
appears in the current issue of the Journal of Studies on Alcohol and
Drugs. In the same issue, a pair from the Center for Medicinal Cannabis
Research at the University of California at San Diego similarly calls for
disinterested experts to guide development of new approaches.

“Developing more robust tools to identify cannabis-impaired drivers in an
unbiased fashion is essential to keeping our roadways safe,” the UC San
Diego authors said.

There’s another wrinkle to the cannabis testing debate: As recently
acknowledged by a U.S. Department of Justice (DOJ) researcher, it’s unclear
whether a person’s THC levels are even a reliable indicator of impairment.

On a podcast last year, Frances Scott, a physical scientist at the National
Institute of Justice (NIJ) Office of Investigative and Forensic Sciences
under DOJ, questioned the efficacy of setting “per se” THC limits for
driving. Ultimately, she said, there may not be a way to assess impairment
from THC levels, as law enforcement does for alcohol.

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.”

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.”

The 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.

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 signed by President Joe Biden, but it missed its
reporting deadline.

Meanwhile, National Transportation Safety Board (NTSB) last year warned
that marijuana rescheduling could create a “blind spot” with respect to
drug testing of federally regulated workers in safety-sensitive
positions—despite assurances from then-U.S. Transportation Secretary Pete
Buttigieg that the cannabis rescheduling proposal “would not alter” the
federal drug testing requirements.

At a House committee hearing, Buttigieg had referenced concerns from ATA
“about the broad public health and safety consequences of reclassification
on the national highway system and its users,” which the trucking
association voiced in a letter to the secretary.

As more states legalize marijuana, a federal report published last year
showed that the number of positive drug tests among commercial drivers fell
in 2023 compared to the year before, dropping from 57,597 in 2022 to 54,464
in the prior year. At the same time, however, the number of drivers who
refused to be screened at all also increased by 39 percent.

Another question found that 65.4 percent of motor carriers believed current
marijuana testing procedures should be replaced with methods that measure
active impairment.

At the time, the report from the American Transportation Research Institute
(ATRI) noted a 65,000-driver deficit in the country and said the fear of
positives over marijuana metabolites—which can remain in a person’s blood
far long after active impairment—may be keeping would-be drivers out of the
industry.

The record-high number of refusals came as the transportation industry
faces a nationwide shortage of drivers, which some trade groups have said
has only been made worse by drug testing policies that risk flagging
drivers even when they’re not impaired on the job.

Current federal law mandates that commercial drivers abstain from cannabis,
subjecting them to various forms of drug screening, from pre-employment to
randomized testing.

In June 2022, meanwhile, an ATRI survey of licensed U.S. truck drivers
found that 72.4 percent supported “loosening” cannabis laws and testing
policies. Another 66.5 percent said that marijuana should be federally
legalized.

Cannabis reform advocates, meanwhile, have also called on federal officials
to change what they call “discriminatory” drug testing practices around the
trucking industry.

A top Wells Fargo analyst said in 2022 that there’s one main reason for
rising costs and worker shortages in the transportation sector: federal
marijuana criminalization and resulting drug testing mandates that persist
even as more states enact legalization.

Then-Rep. Earl Blumenauer (D-OR) sent a letter to the head of DOT in 2022,
emphasizing that the agency’s policies on drug testing truckers and other
commercial drivers for marijuana are unnecessarily costing people their jobs and
contributing to supply chain issues.

The 2022 ATRI report noted that research into the impact of cannabis use on
driving and highway safety is currently mixed, complicating rulemaking to
address the issue. A separate 2019 report from the Congressional Research
Service (CRS) similarly found that evidence about cannabis’s ability to
impair driving is inconclusive.

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.”

The post Current Roadside Tests For Marijuana Impairment Are
‘Pseudoscientific,’ Law Professor Says appeared first on Marijuana Moment.