Laws that legalize recreational marijuana could lead to more road deaths, two new studies suggest, although there are still questions about how they can affect driving behavior.
Previous research has produced mixed results, and the new studies, published Monday in JAMA Internal Medicine, cannot prove that the increase in road deaths found was caused by marijuana use.
A study found more than 75 road deaths each year after retail sales began in Colorado in January 2014, compared to states without similar laws. But it found no comparable change in Washington State.
The other study looked at those states plus two others that allow for the sale of recreational pots, Oregon and Alaska. If each state legalized the sale of recreational marijuana, 6,800 additional people would die in road accidents each year, the researchers calculated. They found an increase of 2 deaths per billion miles traveled compared to 20 states without those laws. That change was slightly higher than in the other study.
Both covered several years of road traffic data from the National Highway Traffic Safety Administration before and at least two years after recreational pot retail sales began in the states investigated. Those sales dates varied from 2014 to 2016.
The studies lack information about whether motorists were stoned in an accident. Marijuana can remain in tissues for several days, so even if toxicological tests discovered it after a fatal accident, that wouldn’t prove the driver had a limitation, said study co-author Magdalena Cerda, a New York University researcher.
It is possible that laws about recreational weed affect the use of other drugs, including alcohol, she noted.
“That’s an open question that we need to answer in further research,” said Cerda.
An editorial magazine said more rigorous research is needed, including studies on how often motorists use drugs.
“Clearly, the introduction of new legal intoxicants could lead to … deaths from impaired driving ability,” the editorial said.
Recreational marijuana is legal in 11 states.
Variations in sales taxes, purchase limits, and other aspects of marijuana laws in each state can play a role in any consequences for road deaths. Also, when the two-state study was conducted, pot shops were closer in Colorado than in Washington, which could have made the drug more readily available, the authors said.
The four-state study led by Dr. Russell Chamber of the New York Medical College took into account unemployment rates, speed limit laws and seat belts. But the authors said other factors they said didn’t affect road deaths.
Follow AP Medical Writer Lindsey Tanner on @LindseyTanner.
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