THURSDAY, Jan. 15, 2015 (HealthDay News) -- Half of young drivers who died in crashes in nine states were under the influence of alcohol, marijuana or both at the time of the accident, a new study finds.
Researchers examined the deaths of nearly 7,200 drivers, aged 16-25, in crashes that occurred between 1999 and 2011 in California, Connecticut, Hawaii, Illinois, New Hampshire, New Jersey, Rhode Island, Washington state and West Virginia.
Those states routinely conduct blood and urine tests of drivers who die in crashes.
More than 50 percent of the drivers tested positive for alcohol (36.8 percent), marijuana (5.9 percent) or both substances (7.6 percent). Those older than 21 were 14 percent more likely to test positive for alcohol, and slightly more likely to test positive for both alcohol and marijuana than those under the legal drinking age.
The study was published online Jan. 12 in the journal Injury Epidemiology.
"Policies related to the use of substances in the United States remain in flux; the rapid changes in marijuana use policy are a good example of this," study leader Katherine Keyes, an assistant professor of epidemiology at Columbia University's Mailman School of Public Health, said in a university news release.
"It's imperative to know whether there will be unintended consequences of changes in policies, including increases or decreases in harm related to other substances that are not the focus of the policy," she added.
Study co-author Dr. Guohua Li, director of Columbia's Center for Injury Epidemiology and Prevention, said in the news release, "Taken together, we found no significant substitution effect between alcohol and marijuana. Rather, an uptick in availability seems to increase the prevalence of concurrent use of alcohol and marijuana."
The U.S. National Library of Medicine has more about impaired driving.