Studies: Smoking Pot Affects Driving Longer Than People Think

2 min read

Feb. 5, 2024 -- Recreational marijuana is now legal in more than 20 states, which may mean there are more marijuana users wondering how soon they can drive safely after getting high.

Studies conducted by the Center for Medicinal Cannabis Research at the University of California, San Diego, show people should wait about 4.5 hours after smoking one joint to get behind the wheel, The Wall Street Journal reported.

However, many study participants wrongly thought they could drive safely much sooner.

In the study published in JAMA Psychiatry, about 200 cannabis users either smoked THC or a placebo, then drove in an automobile simulator. About half the THC users showed driving impairment compared to the placebo group.

“While the THC group generally reported feeling impaired and hesitant to drive at 30 minutes, at 1 hour 30 minutes participants increasingly rated themselves as safe to drive, whereas simulator data indicated ongoing reduced driving performance including being more likely to leave their lane,” the study said. “Although performance was improving at 3.5 hours, recovery was not fully seen until 4.5 hours postsmoking.”

“Even people who are very conscientious and say, ‘I’m not going to drive, I’m too stoned,’ start to believe it’s wearing off,” Tom Marcotte, co-director of the Center for Medicinal Cannabis Research, told The Wall Street Journal. “At least in our analyses, they’re still having issues.”

Other studies show the effects of marijuana last even longer.

Smoking may “impair essential driving skills” for 6 to 8 hours and ingesting an edible will make driving unsafe for 8-12 hours, says a study published in the International Journal of Drug Policy.

“These times can vary from one use context to another. During these impairment periods, driving or similar risk activities should be avoided,” the study said.