The combination of teens’ relative lack of driving experiencing and the use of alcohol or marijuana has led to vehicle accidents becoming the leading cause of death among Americans between the ages of 16 and 19. A study recently published in the Journal of Studies on Alcohol and Drugs has revealed U.S. high school students who in engage in the simultaneous use of alcohol and marijuana are more likely to practice unsafe driving even when they are not impaired.

"It's well known that both drinking and other drug use are linked to risky driving," lead researcher from the University of Michigan's Institute for Social Research, Yvonne Terry-McElrath, said in a statement. "But this suggests that it's not only the frequency of substance use that's important. The patterns of drug use are also related to the risk of unsafe driving."

Terry-McElrath and her colleagues from the university collected data from the National Institute of Drug Abuse’s Monitoring the Future study. Surveys from over 72,000 high school seniors between 1976 and 2011 were used to calculate the number of teens who use both alcohol and marijuana as well as how simultaneous use affects their judgment. Teens who admitted to using both alcohol and marijuana within the past year recorded more tickets, warnings, and traffic accidents. Around 40 percent of teens who reported simultaneous use of alcohol and marijuana received a ticket or warning in the past year, while 30 percent were involved in a traffic accident.

On the plus side, the 78 percent of high school seniors who admitted to using both substances in 1979 has decreased over the years to two-thirds of students in 2011. Twenty-one percent of the teens included in the survey still admitted to using alcohol and marijuana in combination on at least on occasion. Teens who reported simultaneous use were more likely to rack up tickets or be involved in traffic accidents compared to those who drank alcohol or smoked marijuana on their own. Although the research team was unable to give a precise reasoning behind why teenagers who use both alcohol and marijuana are more likely drive recklessly, they did say these teens are bigger risk takers in general.

"Driver's education needs to talk more about the risks, in believable ways—not using inaccurate scare tactics,” Terry-McElrath added. "We often hear the message 'Don't drink and drive,’ but we don't hear much about the risks of using additional substances, either alone or simultaneously with alcohol."

According to the National Institute of Drug Abuse, upward of 10.3 million Americans over the age of 12 admitted to driving under the influence of an illicit drug in 2012, compared to an estimated 29.1 million who reported driving under the influence of alcohol. Second only to alcohol, marijuana is the substance most commonly found in the blood of impaired drivers, fatally injured ones, and drivers involved in a traffic accident.

 

Source: Johnston L, O’Malley P, Terry-McElrath Y. Alcohol and marijuana use patterns associated with unsafe driving among U.S. high school seniors: High use frequency, concurrent use, and simultaneous use. Journal of Studies on Alcohol and Drugs. 2014.