Underage college students often get in car after substance use

Driving after marijuana use or drinking alcohol was common among underage college students, as well as getting in a car with a driver who has used marijuana or who had been drinking, according to study findings published in JAMA Pediatrics.

Jennifer M. Whitehill, PhD, of the department of public health at the School of Public Health and Health Sciences at the University of Massachusetts Amherst, and colleagues evaluated 315 young adults aged 18 to 20 years (56.2% female) from two large universities to determine risk factors associated with underage college students’ driving habits after marijuana use, drinking alcohol or riding with a driver using these substances.

Males had a higher past-28-day prevalence of marijuana use (29.7%) compared with females (13%). The same was true for alcohol use (66.7% of males; 63.8% of females), as well as using both in the past 28 days (23.2% for males; 8.5% for females).

Overall, there was a 6.3% prevalence of driving after marijuana use. Males using marijuana within the past 28 days were more likely to drive after use (43.9%) compared with females (8.7%). Students had a higher risk of driving after marijuana use if they had rode with a marijuana-using driver (RR=5.72; 95% CI, 1.84-17.8), as well as those who drove after drinking (RR=2.45; 95% CI, 1.39-4.31).

However, there was a lower risk among those who were older when first using marijuana (RR=0.78; 95% CI, 0.63-0.97). There was a 22% decreased risk of driving after marijuana use for every 1-year increase in the age at the first use of marijuana.

Thirteen percent of all participants rode with a driver who had used marijuana. More males who used marijuana rode with a driver who had also used marijuana (51.2%) compared with females (34.8%). This risk was increased among those who had drove after using marijuana themselves (RR=4.42; 95% CI, 2.4-8.14).

Just 4.4% of all participants reported driving after drinking. However, 6.8% of those who reported consuming alcohol within the past 28 days reported driving after use.

Participants who drove after drinking also were more likely to ride with a driver who had been drinking (RR=4.73; 95% CI, 2.54-8.08). The risk of riding with a driver who had been drinking also was higher with an increased number of binge drinking days (RR=1.12; 95% CI, 1.08-1.17).

No significant differences were found among driving after marijuana use or alcohol use (P=.29) or riding with a driver who had used either substance (P=.63). However, driving after marijuana use (P=.005) and riding with a driver who used marijuana use (P<.001) were more common than each following alcohol use.

“Despite the limitations of our study, our findings are an important and timely contribution to the literature on older adolescents driving after drug use,” the researchers wrote. “They supplement our knowledge that marijuana use increases the risk of motor vehicle crashes by estimating how common it is for underage students to have taken this risk within the past 28 days.”

In an accompanying editorial, Mark Asbridge, PhD, of Dalhousie University in Nova Scotia, Canada, wrote that the findings bring attention to the problem of using marijuana before operating a vehicle.

“Besides legislation, much work remains to be done to change social norms regarding the acceptability of using marijuana in the context of driving,” he wrote. “Key to this goal is the increased education and awareness of varying stakeholders in public health, transportation, and justice, as well as the general public, particularly young persons, among whom misconceptions about the impairing effects of marijuana on driving are common. Physicians and other health care professionals must also be encouraged to actively remind patients of the increased risk of driving after marijuana use.”

For more information:

Asbridge M. JAMA Pediatr. 2014;doi:10.1001/jamapediatrics.2014.83.

Whitehill JM. JAMA Pediatr. 2014;doi:10.1001/jamapediatrics.2013.5300.

Disclosure: The study was funded by the NIH Common Fund and the National Institute of Child Health and Human Development.