Related Resources NHTSA Public Meetings - Dialogue on Drug-Impaired Driving Drug-Impaired Listening Sessions

Many substances can impair driving, including alcohol, some over-the-counter and prescription drugs, and illegal drugs.

• Alcohol, marijuana, and other drugs can impair the ability to drive because they slow coordination, judgment, and reaction times.
• Cocaine and methamphetamine can make drivers more aggressive and reckless.
• Using two or more drugs at the same time, including alcohol, can amplify the impairing effects of each drug a person has consumed.
• Some prescription and over-the-counter medicines can cause extreme drowsiness, dizziness, and other side effects. Read and follow all warning labels before driving, and note that warnings against “operating heavy machinery” include driving a vehicle.

Impaired drivers can’t accurately assess their own impairment – which is why no one should drive after using any impairing substances. Remember: If you feel different, you drive different.

There are many misconceptions about marijuana use, including rumors that marijuana can’t impair you or that marijuana use can actually make you a safer driver.

Several scientific studies indicate that this is false. Research shows that marijuana impairs motor skills, lane tracking and cognitive functions (Robbe et al., 1993; Moskowitz, 1995; Hartman & Huestis, 2013). A 2015 study on driving after smoking cannabis stated that THC in marijuana also hurts a driver’s ability to multitask, a critical skill needed behind the wheel. 

NHTSA continues to conduct research to better understand the relationship between marijuana impairment and increased crash risk. NHTSA’s Drug and Alcohol Crash Risk Study found that marijuana users are more likely to be involved in crashes. However, the increased risk may be due in part because marijuana users are more likely to be young men, who are generally at a higher risk of crashes.

Research indicates drug prevalence is on the rise among drivers. NHTSA’s 2020 study of seriously or fatally injured road users at studied trauma centers (Thomas et al., 2020) suggested that the overall prevalence of alcohol, cannabinoids and opioids increased during the public health emergency compared to before.

While evidence shows that drug-impaired driving is dangerous, we still have more to learn about the extent of the problem and how best to address it. In January 2018, NHTSA launched a new initiative to address drug-impaired driving. NHTSA’s National Drug-Impaired Driving Initiative brings together experts, including law enforcement officials, prosecutors, substance abuse experts and others, to discuss strategies that can reduce drug-impaired driving.

Driving impaired by any substance—alcohol or other drugs, whether legal or illegal—is against the law in all 50 states and the District of Columbia. Law enforcement officers are trained to observe drivers’ behavior and to identify impaired drivers. Even in states where marijuana laws have changed, it is still illegal to drive under the influence of the drug.

NHTSA’s National Roadside Survey conducted in 2013-2014 (PDF, 173 KB) found that 20 percent of surveyed drivers tested positive for potentially impairing drugs.

Surveys conducted by NHTSA show the number of drivers testing positive for marijuana increased between 2007 and 2014. In 2007, NHTSA’s National Roadside Survey (PDF, 1 MB) found that 8.6 percent of weekend nighttime drivers tested positive for marijuana. In the 2013-2014 survey, 12.6 percent of weekend nighttime drivers tested positive for marijuana. That’s a 48-percent increase in less than 10 years.

While the presence of a drug in a driver’s system doesn’t necessarily mean that they’re impaired, these findings show the importance of raising awareness about the risks of drug-impaired driving.

We can all save lives by making smarter choices.

• Plan ahead for a sober driver, if you plan to use an impairing drug.
• Don’t let friends get behind the wheel if they’re under the influence of drugs.
• If you’re hosting a party where alcohol or other substances will be used, it’s your job to make sure all guests leave with a sober driver.
• Always wear your seat belt—it’s your best defense against impaired drivers.