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Stimulant use among teens are at higher risk of driving impairment

Higher substance use frequency was significantly and positively linked to unsafe driving

A study from researchers at the University of Michigan's Institute for Social Research unsafe driving was significantly and positively associated with simultaneous use of alcohol and marijuana among teens.
GettyImages/Arthur Carlo Franco

In a new article from the Institute of Social Research, University of Michigan Ann Arbor, researchers examine noncausal associations between high school seniors, alcohol and marijuana use status and rates of self-reported unsafe driving in the past 12 months.

Yvonne Terry-McElrath, lead researcher of the University of Michigan's Institute for Social Research and colleagues examined data from 72,053 students gathered from annual surveys of U.S. 12th graders from 1976 to 2011. Two aspects of past 12 month of alcohol and marijuana were examined; a) frequency, students reported alcohol, marijuana and hashish use as 0 occasions 1–2, 3–5, 6–9, 10–19, 20–39, and 40 or more occasions . Marijuana and hashish were combined and referred to as marijuana and b) status as a non-user, single substance user, concurrent user, or simultaneous user.

Measures of past-12-month unsafe driving included any tickets/warnings or accidents, as well as tickets/warnings or accidents following alcohol or marijuana use.

Researchers examined whether an individual’s substance use frequency and simultaneous use status had differential associations with their rate of unsafe driving.

The results showed 103,129 total cases were available from the questionnaire form including the SAM (simultaneous alcohol and marijuana); use of both substances in combination at the same time.

Among the total cases 90% (93,036) valid data for past-12-month marijuana and alcohol use as well as SAM use status. Among those cases 88% (82,003) had tickets/warnings or accidents.

"It's well known that both drinking and other drug use are linked to risky driving.” "But this suggests that it's not only the frequency of substance use that's important," Terry-McElrath said. "The patterns of drug use are also related to the risk of unsafe driving."

However, over time one-third of high school seniors had said they had not used either marijuana or alcohol over in the past year compared to only 12% in 1979.

Higher substance use frequency (mainly alcohol frequency) was significantly and positively linked with unsafe driving.

According to Terry-McElrath “It's not clear why those teenagers were at increased risk.” She said one possibility is that they are bigger risk takers in general. But it's also possible that using both drugs together impairs teenagers' driving—and judgment—to a greater degree.

In their conclusion the researchers write “This article expands the knowledge on individual risk factors associated with unsafe driving among teens. Efforts to educate U.S. high school students (especially substance users), parents, and individuals involved in prevention programming and driver’s education about the increased risks associated with various forms of drug use status may be useful.”

In closing Terry-McElrath said it's important to make kids and the public in general aware of the risks of simultaneous drug use.

"Driver's education needs to talk more about the risks, in believable way, not using inaccurate scare tactics, she commented.

More broadly, she added, media messages about unsafe driving should go beyond alcohol.

Terry-McElrath noted "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."

This paper appears in the Journal of Studies on Alcohol and Drugs.

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