Current field sobriety tests administered by trained law enforcement officers may not be enough to identify drivers who are driving under the influence of cannabis, according to a report published yesterday in JAMA Psychiatry.
“Road safety is a critical issue in an era of increasing cannabis legalization,” wrote Thomas D. Marcotte, Ph.D., of the Center for Medicinal Cannabis Research at the University of California, San Diego, and colleagues. “In the field, impairment is determined via observation of driving behavior (i.e., vehicle in motion), driver interviews, and field sobriety tests …, which examine abilities, such as balance, coordination, divided attention, and eye movements.” However, questions remain about the ability of field sobriety tests (based on validation with alcohol) to capture the level of intoxication under the influence of cannabis.
Marcotte and colleagues recruited licensed drivers aged 21 to 55 years who had used cannabis at least four times in the past month and who reported driving at least 1,000 miles in the past year. Drivers who had a history of traumatic brain injury, had significant physical or psychiatric conditions, or had been diagnosed with a substance use disorder in the past year were excluded from the trial.
For the double-blind, placebo-controlled trial, 199 participants were assigned to one of three groups; on the experiment day, they received one cannabis cigarette containing either 13.4%, 5.9%, or 0.02% THC content. The last group made up the placebo group.
Field sobriety tests, including the Walk and Turn (WAT), One Leg Stand (OLS), and Finger to Nose (FTN) tests, were administered to the study participants by certified California Highway Patrol Drug Recognition Evaluators approximately 1, 2, 3, and 4 hours after the participants smoked the assigned cigarette. The participants also completed multiple 25-minute driving simulations for approximately four hours after smoking.
The final sample included 184 participants. While the officers classified 81% of the THC group as impaired based on the results of the first field sobriety tests, they also classified nearly half of the participants in the placebo group as impaired. The THC group had a substantially higher percentage of participants who failed to adequately perform on some component of the tests compared with the placebo group overall, the authors reported. Impairment declined in both groups over time. “Worse simulator performance in the THC group was uniquely associated with clues on the WAT, OLS, and FTN tests and with total clues,” Marcotte and colleagues wrote.
They concluded, “The findings of this study suggest that (1) [field sobriety tests] are useful adjuncts but do not provide strong objective evidence of THC-specific impairment and (2) additional efforts to validate existing methods and provide law enforcement with new, effective tools for identifying impairment are needed.”
In an accompanying editorial, Johannes G. Ramaekers, Ph.D., of Maastricht University in the Netherlands and colleagues wrote: “[C]urrent legislators can only choose between tests for detecting (recent) cannabis exposure, behavioral tests whose results inaccurately predict driving impairment, or a combination of both, even though their indication of cannabis impairment is scientifically unjustified and will be, understandably, legally challenged. Yet, aside from not wanting unjust convictions for driving under the influence, we must also remember that cannabis does have the potential to cause impairment and that in such cases drivers should be barred from the road.”
Despite attempts to develop reliable roadside tests for cannabis impairment, none have been validated yet. This lack of reliable tests to measure cannabis impairment has also impacted studies designed to assess the risk of cannabis on traffic accidents. “Standard tests of cannabis impairment should be sensitive to the large variation in cannabis products and product formulations that have flooded the consumer market and should also be able to reflect interindividual variations in the response to acute cannabis intoxication.”
For related information, see the Psychiatric News Alert “More Youth Drive Under the Influence of Cannabis Than Alcohol.”
(Image: iStock/Simon Gallagher)
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