Columbia: States that enacted medical marijuana laws, on average, experienced reductions in traffic fatalities, according to a study by researchers at Columbia University’s Mailman School of Public Health. Overall, states that passed medical marijuana laws saw an 11 percent reduction in traffic fatalities, on average, after enacting the laws, and had 26 percent lower rates of traffic fatalities compared with states without the laws. The findings are published online in the American Journal of Public Health.
in traffic fatalities greatly impacted those between the ages of 15 and
44 and were especially striking among those aged 25 to 44 years, a
group representing a high percentage of those registered patients for
medical marijuana use.
Specifically, the researchers observed
an 11 percent reduction of among those aged 15 to 24 years, 12 percent
for ages 25 to 44, and 9 percent for those 45 years and older.
Operational dispensaries were also associated with a significant
reduction in traffic fatalities in those aged 25 to 44 years at 5
Lacking was strong evidence suggesting reductions among
those aged 45 years and older, which is also a group overrepresented in
the population of patients registered in state medical marijuana
programs. “This finding suggests that the mechanisms by which medical
marijuana laws reduce traffic fatalities mostly operate in those younger
adults, a group also frequently involved in alcohol-related traffic
fatalities,” said Julian Santaella-Tenorio, a doctoral student in Epidemiology
at the Mailman School of Public Health. In 2004 and 2013, 47 percent of
fatally injured drivers with a blood alcohol content of 0.08 or greater
were 25 to 44 years old.
The researchers based their findings
on data for 1985-2014 from the Fatality Analysis Reporting System, a
nationwide census of traffic fatalities information maintained by the
National Highway Traffic Safety Administration. The association between
medical marijuana laws and traffic fatalities for drivers, passengers,
cyclists, and pedestrians was examined for each state enacting the laws.
They also evaluated the link between marijuana dispensaries and traffic
fatalities. Overall, a total of 1.22 million deaths were attributed to
traffic crashes occurring in the 50 states during the study period.
all states with medical marijuana laws experienced reductions in
traffic fatality rates, and a few states actually experienced increases.
In California, after an initial immediate reduction of 16 percent in
traffic fatalities and in New Mexico, after an immediate post-law
reduction of 17.5 percent, the laws were actually associated with
gradual increases in fatality rates. “These findings provide evidence of
the heterogeneity of medical marijuana laws and indicate the need for
further research on the particularities of implementing the laws at the
local level. It also indicates an interaction of medical marijuana laws
with other aspects, such as stronger police enforcement, that may
influence traffic fatality rates,” noted Santaella-Tenorio.
is also possible that states with medical marijuana laws and lower
traffic fatality rates may be related to lower levels of
alcohol-impaired driving behavior in these states,” noted Silvia Martins, MD, PhD, associate
professor at the Mailman School and senior author. “We found evidence
that states with the marijuana laws in place compared with those which
did not, reported, on average, lower rates of drivers endorsing driving
after having too many drinks. We can also point to other characteristics
such as the strength of public health laws related to driving,
infrastructure characteristics, or the quality of health care systems,
as a partial explanation for these findings.”
linking medical marijuana laws and traffic fatalities lays the
groundwork for future studies on specific mechanisms,” said
Santaella-Tenorio. “We also expect another area of study will be the
association between the laws and nonfatal traffic injuries.”
are Christine M. Mauro, Melanie M. Wall, June H. Kim, Katherine M.
Keyes, and Deborah S. Hasin—all of the Mailman School of Public Health;
Magdalena Cerdá, University of California, Davis; and Sandro Galea,
This work was supported by the National
Institute on Drug Abuse (grants R01DA037866, R01DA034244, T32 DA031099,
K01 DA030449), and the National Institute on Alcohol Abuse and
Alcoholism (grant K01 AA021511). Dr. Santaella-Tenorio is funded by the
J. William Fulbright and the Colciencias doctoral scholarships.