Some 33% of drivers who drink alcohol and use marijuana simultaneously report getting behind the wheel within two hours of doing so, according to a recent study from the Insurance Institute for Highway Safety (IIHS).

That fact is a serious concern because evidence suggests the combination of alcohol and marijuana worsens driving performance more than either substance by itself. For example, an earlier IIHS study of patients who were at a hospital emergency room due to a motor vehicle crash only showed an increased crash risk associated with marijuana when it was combined with alcohol.

Moreover, recent research shows that young adults are more likely to drive or take other risks after using both substances than after consuming marijuana alone, notes IIHS. But just how frequently do people consume both substances simultaneously?

IIHS surveyed more than 3,000 adult drivers across Connecticut, Delaware, New York, North Carolina, South Carolina, and Virginia about their behaviors with alcohol, marijuana, and driving. Noteworthy, Connecticut, New York, and Virginia all legalized marijuana for recreational use in 2021, while it remains illegal in Delaware, North Carolina, and South Carolina.

Overall, 71% of drivers in the six states reported past-year drinking, 24% reported past-year marijuana use, and 11% reported past-year simultaneous use of both substances. As it concerns imbibing two hours or less before driving, some 28% of those drinking alcohol, 41% of those using marijuana, and 33% of those using both substances reported doing so. 

Gender differences are noteworthy as well. Men were more likely than women to use either substance before getting behind the wheel. Approximately 25% of men reported drinking and driving, compared with just 15% of women. Twelve percent of males reported using marijuana and 5% reported using both marijuana and alcohol before driving, compared with 8% and 3% of females.