The most recent national estimates of drivers who operate a car under the influence of marijuana put the numbers in the millions, according to a new report from the US Centers for Disease Control and Prevention.

Thursday's Morbidity and Mortality Weekly Report found that in 2018, 12 million American adults said they had driven under the influence of weed in the 12 months prior to the survey. About 2.3 million said they had driven under the influence of illicit drugs such as cocaine or methamphetamine.

That breaks down to 4.7% of Americans driving under the influence of weed and 0.9% driving under the influence of the other drugs. The percentage is much smaller than the number of drivers who said they drove under the influence of alcohol. In 2018, 8% of drivers said they had a drink before driving at some point during the previous year.

Male drivers were more likely to report using marijuana or illicit drugs than female drivers. The people most likely to say they used pot before driving were people in the 21-25 age group. The second highest group to report using weed were people between the age of 16 and 20, the youngest category of drivers to qualify for a license. That, the authors say, "is of special concern," since newer drivers already have a heightened risk of causing accidents because of their inexperience on the road.

The demographic most likely to drive under the influence of marijuana are non-Hispanic multiracial persons at 9.2%, the report found.

Weed is legal in a growing number of states, but driving under its influence is not. Earlier studies have shown that using marijuana can seriously alter a driver's judgment, perception, ability to think clearly and reaction time.