Marijuana and Alcohol Influence Half of Fatal Crashes Involving Young Drivers

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Half of the young victims involved in fatal crashes in nine U.S. states were under the influence of alcohol, marijuana, or both, according to a new study published in the journal Injury Epidemiology.

Columbia University’s Mailman School of Public Health researchers analyzed 7,191 fatal accidents from 1999 to 2011 involving drivers between the ages of 16 and 25 who died within one hour of the crash, in order to gauge how potential policy changes might influence substance use among adolescents and young adults. The nine states examined — California, Connecticut, Hawaii, Illinois, New Hampshire, New Jersey, Rhode Island, Washington State and West Virginia — each routinely perform toxicological tests on the blood or urine of fatal accident victims.

“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,” said Katherine M. Keyes, PhD, assistant professor of Epidemiology and lead author, in a press 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.”

The study found that, overall, more than half (50.3%) of those who died had alcohol, marijuana, or both in their systems at the time of the accident. Of those who did, 7.6% were under the influence of both, 5.9% were under the influence of marijuana and 36.8% were under the influence of alcohol, which also happens to be the number one drug problem affecting the country.

The researchers then examined whether 21-year-olds, who were allowed to consume alcohol legally, used substances differently than their underage counterparts. They found that while alcohol consumption had increased by 14%, marijuana usage had actually decreased among those who had only the drug. The use of both marijuana and alcohol at the same time had increased only marginally.

“Taken together, we found no significant substitution effect between alcohol and marijuana,” said the Center for Injury Epidemiology and Prevention’s director and co-author of the study Guohua Li. “Rather, an uptick in availability seems to increase the prevalence of concurrent use of alcohol and marijuana.”

Essentially, the more available the substance, the more likely it is to be used, but there’s no significant substitution between the two. It seems that people aren’t substituting one for the other or vice versa based on legality or any other factor.

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