Vast majority of cannabis users drive afterwards, report says. What to know about the risks.
A new study has found that more than 84% of cannabis users smoke, eat, drink or vape marijuana within eight hours of getting behind the wheel.
The AAA Foundation for Traffic Safety published a report last week which found that 84.8% of cannabis users − 2,000 respondents from eight states − drove within eight hours of consumption, and 53% of these respondents drove within an hour or less of consumption.
As marijuana continues to be legalized throughout the country − now recreationally legal in 24 states − researchers and law enforcement authorities are quickly looking to better understand how marijuana affects the body and brain. Even in the states where marijuana is medically and recreationally legal, it remains illegal for drivers to get behind the wheel after consuming the drug, yet there is not a standard method for law enforcement agencies to identify or test marijuana impairment.
Here's what to know about the study's findings and just how much marijuana affects drivers.
Data on motor vehicle accidents and deaths related to cannabis consumption varies, especially from state to state, but generally, the legalization of marijuana has led to an uptick, studies show.
Studying death certificates between 2009-2019, the University of Illinois Chicago found a 10% increase in motor vehicle death in four states where marijuana was legalized recreationally − Colorado, Oregon, Alaska and California.
More: The movement to legalize psychedelics comes with high hopes, and even higher costs
Studying the same 10-year period, another study published in the Journal of Studies on Alcohol and Drugs found that throughout the entire U.S., the legalization of recreational marijuana was associated with a 6.5% increase in injury crashes and a 2.3% increase in fatal crashes.
Though marijuana-related motor vehicle accidents may be on the rise, the numbers hardly compare to accidents and deaths related to alcohol impairment.
Michael Greger, a founder of the American College of Lifestyle Medicine, wrote that while cannabis use may double or triple the risk of car crashes, alcohol multiples the risk between six to 15 fold.
Research on just how cannabis affects a driver is quite inconclusive, as much is dependent on how often and much a person consumes marijuana, the type of marijuana consumed, and the marijuana's potency, or THC content. A person's metabolism, body weight and overall tolerance also impacts effects on the body and mind.
Generally, a frequent marijuana user who consumes the same type and potency of product may be less susceptible, or affected, by marijuana's psychoactive effects than a first-time user.
"Patients who take cannabinoids at a constant dosage over an extensive period of time often develop tolerance to the impairment of psychomotor performance," a 2012 study published by German medical magazine, Deutsches Ärzteblatt states.
The mode of consumption also plays a large role on how marijuana affects a user. A study published in the medical journal Clinical Chemistry states that the psychoactive effects of cannabis inhalation (like smoking) begins within minutes and peaks within three hours. On the other hand, oral administration (like eating an edible), can take up to an hour to begin and last up to eight hours.
In the case of the recently published AAA study, 50% of respondents said they consumed marijuana the same day as completing the survey, and more than 44% said they consumed marijuana multiple times a day. The majority of respondents said they consumed dried flower (68.6%) or edibles (64.1%).
Is marijuana the same as cannabis? What is THC? Terms to know as states vote on legal weed
As for how respondents thought use affected their driving, 46.9% said they believed they drove the same as when they were unimpaired, and the majority said drowsiness, brain fog and slow reaction times were their most common symptoms while driving under the influence of cannabis.
A 2019 study published by the international journal Drug Alcohol Dependence supported these symptoms. Of 91 respondents who participated in a simulated driving test, the average driving speed "significantly differed" between those who had not smoked cannabis and those who had. Those who drove 30 minutes after smoking cannabis drove slower. Another study, published by the medical journal JAMA Network, found the same thing: those who smoke marijuana decrease their driving speed.
Yes, cannabis and alcohol can affect a driver's performance differently. Commonly, drivers under the influence of cannabis drive slower than those under the influence of alcohol, studies show.
A 2024 study published in the academic journal Traffic Injury Prevention found that 53 regular cannabis users, who were under the influence, spent "more time" at speeds "significantly" below the speed limit during a simulated driving test. In contrast, the study found that 18 of these users, under the influence of solely alcohol, spent 40% or more of the time above the speed limit.
Why is this the case? Alcohol impairment often leads to overconfidence, which may be the result of speeding, weaving through traffic and ignoring traffic signals, the Colorado Department of Transportation states. On the other hand, cannabis impairment may lead to anxiety and paranoia, which may make a driver more cautious, wanting to drive slower. Both types of impairment can affect judgement, coordination and reaction time, which increases the risk of a crash.
No. In all 50 states, even those where marijuana is legal, it is illegal to drive under the influence.
Greta Cross is a national trending reporter at USA TODAY. Follow her on X and Instagram @gretalcross. Story idea? Email her at gcross@usatoday.com.
This article originally appeared on USA TODAY: Majority reports driving while high. Here's what to know about risks.
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