"Alcohol and cannabis are two of the most common substances involved in impaired driving and motor vehicle crashes" in the United States, said Priscila Dib Gonçalves, the study's first author, in a news release
. Gonçalves is a postdoctoral research fellow in the epidemiology department at Columbia University's Mailman School of Public Health.
Having alcohol or cannabis in one's system while driving can impair cognitive function and physical movements related to those mental processes, impacting driving performance, according to prior research
Use of both substances together has led to more severe and fatal driving-related outcomes when compared to how many of these outcomes resulted from the use of either substance alone, especially among younger people, previous research
found. But there hadn't been a nationally representative study of these associations among adults ages 16 and older until now, according to the new study's authors.
The authors used data from more than 34,000 drivers who answered questions about their drug use and driving habits for the National Survey on Drug Use and Health between 2016 and 2019. More than half of participants reported they hadn't driven under the influence of alcohol or cannabis, while 42.3% said they had.
Over 8% of survey participants reported daily alcohol use, and nearly 20% used cannabis daily. Close to 28% of participants reported simultaneous use of both drugs, which the study defined as "using marijuana or hashish at the same time or within a couple hours of their last alcohol use."
"The high prevalence of people using both alcohol and cannabis who also reported driving under the influence in the past year was striking," said the study's senior author Pia Mauro, an assistant professor of epidemiology at Columbia University's Mailman School of Public Health. "Two in 5 people in the sample reported driving under the influence, which indicates that it is not a rare occurrence among people using these substances."
People who simultaneously used cannabis and alcohol were nearly three times more likely to drive under the influence of cannabis, and three and a half times more likely to drive under the influence of both drugs, the authors found. The study
published Tuesday in the American Journal of Preventive Medicine.
"In the context of increasing daily cannabis use among adults, our findings connecting daily cannabis use and DUI raises public health concerns," Mauro said in a news release. "Population changes in cannabis use frequency that may be associated with health hazards, including daily use, need to be continuously monitored."
Avoiding unsafe driving
Of all study participants, 57% to 68% were male, White, had a family income of $40,000 or less, and lived in a state where medical cannabis was legal. Since details on drug use and driving under the influence were according to participants' own reports, the authors didn't have data on the actual levels of cannabis or alcohol in participants' systems, or whether any participants were cited for DUI or involved in any driving incidents.
However, "when people use alcohol and cannabis (such as on a daily basis) or at the same time, there may be more potential opportunities to drive while impaired," Mauro told CNN.
Previous research "has shown we are making progress in lowering the likelihood that drivers will drink and drive. This study shows that most DUI now is not related to alcohol use alone," said Yvonne Terry-McElrath, a senior research associate at the University of Michigan's Institute for Social Research, via email. Terry-McElrath wasn't involved in the study.
"There is a strong need for accurate information on the degree to which cannabis and simultaneous use impact driving skills and ability," she added.
People who use alcohol or cannabis should know that these drugs can cause "a decrease in someone's ability to respond to things that are happening on the road, even at lower levels" of use, said Linda Degutis, a lecturer at the Yale School of Public Health and past president of the American Public Health Association, who wasn't involved in the study.
"You don't need to be at the point of feeling drunk in order to have impairment on your ability to respond to, let's say, changes on the road or a pedestrian walks into the road or any kind of situation that you need to react to relatively quickly," Degutis said.
If you have recently used cannabis or alcohol and are considering traveling, have someone who isn't intoxicated do the driving, Degutis said. You could also use rideshare or public transportation, or simply not travel if it's not essential.