Teenagers who drink alcohol and smoke marijuana together may be at increased risk for unsafe driving, a study shows.
"Both drinking and other drug use are linked to risky driving. But this new research suggests that it is not only the frequency of substance use that is important. The patterns of drug use are also related to the risk of unsafe driving," explained Yvonne Terry-McElrath from University of Michigan's institute for social research.
The study of US high school seniors found that teenagers who had used both drugs in the past year had higher rates of traffic tickets/warnings and car accidents.
The findings come from surveys of more than 72,000 US high school seniors.
At particular risk were kids who used alcohol and marijuana at the same time: They were about 50 to 90 percent more likely to admit to unsafe driving than their peers who did not drink or smoke pot.
Although both drinking and marijuana use declined over time but still a "significant number" of students were using both drugs in 2011, Terry-McElrath added.
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Roughly 40 percent of teenagers who used both drugs together received a traffic ticket or warning in the past year while about 30 percent had been in an accident.
Media messages about unsafe driving should go beyond alcohol.
"We often hear the message 'don't drink and drive'. But we do not hear much about the risks of using additional substances, either alone or simultaneously with alcohol," she noted.
The study has been published in the Journal of Studies on Alcohol and Drugs.