Marijuana legalization in the United States appears to be driving an increase in car crash deaths due to a jump in "intoxicated driving," researchers say.
In 4 out of 7 states that legalized recreational cannabis, deaths from car crashes rose 10%, according to the University of Illinois Chicago study. On a brighter note, suicide and opioid overdose deaths declined in the states that legalized recreational marijuana.
"Overall, this study provides evidence of the potential harms and benefits of legalizing recreational markets," said lead author Samantha Marinello, a postdoctoral research associate in the university's School of Public Health.
"A potential unintended consequence of legalizing recreational cannabis is an increase in intoxicated driving and crash deaths," she added. "Therefore, there is a need for policies and public health initiatives to reduce driving under the influence."
As of December, 21 states and Washington, D.C., allowed the sale of recreational marijuana to adults age 21 and older.
Where folks can legally toke, it's likely people are driving under the influence of cannabis or cannabis in combination with another drug such as alcohol, Marinello said. However, this study cannot prove cause and effect, she added.
Some people may believe driving high is safe. "Studies of cannabis users have found safety perception is a strong predictor for cannabis-intoxicated driving," Marinello said.
There is evidence that many cannabis users do not believe cannabis negatively affects their driving, agreed Russ Martin, senior director of policy and government relations at the Governors Highway Safety Association.
"In fact, some believe cannabis consumption improves it," he said. "The more often people consume cannabis, the less dangerous they consider driving under the influence of cannabis to be."
The association does not take a position for or against cannabis legalization for adults, Martin said. "But we need to make sure we are ready for any impacts on the roadways."
The study team looked at car-crash fatalities in Alaska, California, Colorado, Massachusetts, Nevada, Oregon and Washington after legalization of recreational marijuana (as distinct from medical marijuana). They used death certificate data from 2009 to 2019.
They found significant increases in crash deaths in Colorado (16%), Oregon (22%), Alaska (20%) and California (14%).
No evidence was found that recreational marijuana affected suicides, which is important because marijuana use is linked with depression and suicidal thoughts, the authors noted.
Recreational marijuana was also tied to an 11% reduction in opioid overdose deaths in all seven states. These reductions ranged from 3% to 28%.
Marinello believes more enforcement is important, as well as raising awareness about the dangers of cannabis-impaired driving.
"There is a substantial amount of evidence that cannabis use impairs driving ability -- increasing reaction time and lane weaving -- and impairs cognitive functions, such as sustained and divided attention," Marinello said.
"It is also critical for the public to know that using alcohol and cannabis together worsens driving ability to a greater extent than either substance alone," she said.
One expert added that driving under the influence of alcohol poses a greater danger than marijuana.
"We need to put into perspective that magnitude of risk from cannabis intoxication is many-fold less than that of alcohol in terms of both fatal and non-fatal motor vehicle accidents," said Dr. Godfrey Pearlson, a professor of psychiatry and neuroscience at Yale University School of Medicine. He was not involved in the study.
On the other hand, Dale Gieringer, director of California NORML, which lobbies for legalizing cannabis, doesn't think this study says anything useful about the effects of marijuana legalization on driving safety. "There exist far too many uncontrolled variables in broad interstate comparisons like this to come to meaningful results," he said.
Accident rates vary greatly from year to year, Gieringer said. "Other studies, such as from Canada, have found no impact at all of legalization on accident rates, and still others have found improved accident rates in states with legal medical marijuana. I take such studies with a grain of salt," he noted. "I would note that the Netherlands, where marijuana has been de facto legal for over 40 years, ranks at or near the top in road safety in the EU, far better than its neighbors, Belgium and Germany."
The report was published online in the March 2023 edition of the journal Social Science & Medicine.
For more on marijuana and driving, see the U.S. Centers for Disease Control and Prevention.
SOURCES: Samantha Marinello, MS, PhD candidate and research associate, Division of Health Policy and Administration, School of Public Health, University of Illinois Chicago; Godfrey Pearlson, MBBS, professor, psychiatry and neuroscience, Yale University School of Medicine, New Haven, Conn.; Dale Gieringer, PhD, director, California NORML; Russ Martin, senior director, policy and government relations, Governors Highway Safety Association; Social Science & Medicine, online, Jan. 16, 2023