Can field sobriety tests identify drivers under the influence of cannabis?
UC San Diego scientists evaluate how accurate law-enforcement administered field sobriety tests are at measuring cannabis exposure and impairment
Peer-Reviewed PublicationIMAGE: CANNABIS IS THE ILLICIT DRUG MOST FREQUENTLY FOUND IN THE BLOOD OF DRIVERS INVOLVED IN MOTOR VEHICLE CRASHES, INCLUDING FATAL ONES. view more
CREDIT: PHOTO BY ELSA OLOFSSON ON UNSPLASH
Road safety is a critical issue in an era of increasing cannabis legalization. Cannabis is known to impair reaction time, decision-making, coordination and perception—skills necessary for safe driving. In the last three years, California has seen a 62% increase in the number of fatal crashes involving drug-related impairment.
Unlike the association of blood alcohol concentrations with impairment, tetrahydrocannabinol (THC) blood concentrations do not correlate with driving performance. Law enforcement officers instead rely on behavioral tests to determine a driver’s level of impairment. However, these field sobriety tests were primarily validated based on alcohol ingestion, so how useful they are in detecting cannabis impairment remains unclear.
In a study published August 2, 2023 in JAMA Psychiatry, researchers at the University of California San Diego Center for Medicinal Cannabis Research performed a double-blind, placebo-controlled randomized clinical trial to evaluate how accurate field sobriety tests are in identifying drivers under the influence of THC. The results showed that tests administered by law enforcement officers could differentiate between individuals who had consumed THC versus those who had not at certain time points. Still, the overall accuracy of the tests may be insufficient to denote THC impairment on their own.
“Driving is a complex task that requires intact attention and motor skills to stay safe,” said first author Thomas Marcotte, PhD, professor of psychiatry at UC San Diego School of Medicine and co-director of the Center for Medicinal Cannabis Research at UC San Diego. “While cannabis can be impairing, the effects vary for each individual. There is thus a public health need to confirm that evaluations of impairment are effective and unbiased, and this study is an important step towards that goal.”
The study included 184 adult cannabis users between the ages of 21 and 55. During the experiment, 63 participants received a placebo cannabis cigarette while 121 participants received a THC cannabis cigarette. Participants who consumed the THC reported a median highness level of 64 on a scale of 0 to 100, suggesting the content was sufficient to achieve significant intoxication.
Highly trained law enforcement officers then performed field sobriety tests to examine abilities such as balance, coordination, divided attention and eye movements. These include the Walk and Turn, One Leg Stand, Finger to Nose, Lack of Convergence and Modified Romberg tests. The tests were performed at four different time intervals, roughly one, two, three and four hours after smoking.
The results showed that officers classified a significantly higher proportion of participants in the THC group as being impaired based on the field sobriety tests compared to the placebo group at three of the four time points measured. For example, one hour after smoking, they labeled 98 participants (81%) from the THC group as being impaired based on their performance, and 31 participants (49%) from the placebo group. But regardless of their actual assignment (THC vs. placebo), officers suspected that 99% of those who failed the tests had received THC.
Study participants also completed a driving simulation, and their performance was significantly associated with the results of select field sobriety tests, though officers were not privy to this information.
The researchers concluded that existing field sobriety tests may be sensitive enough to detect those under the influence of cannabis. However, the substantial overlap in poor test performance between the placebo and THC groups, and the high frequency at which officers suspected this was because of THC consumption, suggest that field sobriety tests alone may be insufficient to identify THC-specific driving impairment.
The authors note that officers in the field would be equipped with more information by interviewing the driver and observing their driving ability, so pairing the field sobriety tests with this additional information could prove more successful in an overall determination of whether a driver is impaired.
“Field sobriety tests are useful additions to overall evaluations of drivers, but are not accurate enough on their own to determine THC impairment,” said Marcotte. “New effective measures for identifying cannabis impairment are needed to ensure the safety of all drivers on the road.”
The UC San Diego Center for Medicinal Cannabis Research has now partnered with the California Department of Motor Vehicles and the California Highway Patrol on a follow-up study to test various methods of detecting cannabis-impaired driving. The study aims to recruit 300 participants and is set to begin in late summer 2023.
Co-authors include: David J. Grelotti, Kyle F. Mastropietro, Raymond Theodore Suhandynata, Igor Grant, Anya Umlauf, Emily G. Sones and Robert L. Fitzgerald, all at UC San Diego, as well as Marilyn A. Huestis at Thomas Jefferson University.
The study was funded by the State of California via Assembly Bill 266, agreement 907.
Full study: doi:10.1001/jamapsychiatry.2023.2345
Cannabis poisonings rise after legalization, new review concludes
A new meta-analysis (an analysis of past research) published by the scientific journal Addiction has found that cannabis legalisation is associated with increased rates of cannabis poisoning. The risk of cannabis poisoning was higher among studies that focused on children.
Cannabis poisoning occurs when too much cannabis is consumed at one time. The effects of cannabis poisoning include lethargy, drowsiness, dizziness, hypertension, palpitations, tachycardia (elevated heart rate), nausea, vomiting, irritability, agitation, coma, and slowing of the central nervous system. Cannabis use in children (usually inadvertent) is of particular concern as children have the potential for severe toxicity, including coma and neurological and cardiovascular effects.
The analysis pooled the results of 30 studies, including ten abstracts from major clinical toxicology conferences. The studies reported a general rise in the rate of cannabis poisoning after cannabis legalisation or decriminalisation. However, results among the studies are highly heterogenous, and most of the evidence comes from the USA and Canada, which might not apply in other countries that have legalised or decriminalised cannabis. Studies that focused on the medical use of cannabis reported a higher risk of poisoning and were less heterogenous than those that included the recreational use of cannabis. Studies that did not report a statistically significant change for overall poisoning often found increases among subgroups, such as children or intensive care admissions.
Senior author Dr. Rose Cairns, from the University of Sydney, says, “Although the results of the studies are varied, almost all of them point to an increase in cannabis poisoning following a change to cannabis laws. The likely explanation is that legislation has increased the use of cannabis, which has also increased poisoning. For example, the modification of cannabis laws could have increased the perceived acceptability of cannabis use (if it’s legal, it must be safe), thereby increasing use.
“Increased availability and use of edibles (gummies and chocolates, for example) appears to be an important driver of the increase in poisonings, particularly among children. Edible cannabis has a higher risk of poisoning because people tend to consume larger quantities, and the effects of cannabis take longer to show up when ingested than they do when smoked. This is concerning because edibles are especially attractive to children.”
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For editors:
This paper is available Open Access from the Wiley Online Library: https://onlinelibrary.wiley.com/doi/10.1111/add.16280 or by contacting Jean O’Reilly, Editorial Manager, Addiction, jean@addictionjournal.org.
To speak with co-author Professor Nicholas Buckley please contact him via Michelle Blowes, University of Sydney Media and PR Adviser, by email (michelle.blowes@sydney.edu.au) or mobile (+61 (0)478 303 173).
Full citation for article: Allaf S, Lim JS, Buckley NA, and Cairns R. The Impact of Cannabis Legalisation and Decriminalisation on Acute Poisoning: A Systematic Review. Addiction. 2023. DOI: 10.1111/add.16280
Funding: Rose Cairns is supported by an NHMRC Investigator Grant (ID: 1196516), Nicholas Buckley is supported by an NHMRC investigator Grant (ID: 2007726).
Declaration of interests: None.
Addiction is a monthly international scientific journal publishing peer-reviewed research reports on alcohol, substances, tobacco, and gambling as well as editorials and other debate pieces. Owned by the Society for the Study of Addiction, it has been in continuous publication since 1884.
JOURNAL
Addiction
METHOD OF RESEARCH
Meta-analysis
SUBJECT OF RESEARCH
People
ARTICLE TITLE
The Impact of Cannabis Legalisation and Decriminalisation on Acute Poisoning: A Systematic Review
ARTICLE PUBLICATION DATE
27-Jul-2023
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