Comment: Buzzed behind the wheel a growing threat in U.S.

By Andrew Yockey / For The Conversation

In October 2023, an unthinkable tragedy unfolded in Coleman, Wis.: An 8‑month‑old girl lost her life when a driver, impaired by cannabis, ran a stop sign and crashed into another vehicle. In February 2025, the driver pleaded guilty to negligent vehicular homicide and drugged driving with a minor passenger; and now faces up to 10 years behind bars.

These preventable circumstances highlight a stark reality: Drugged driving can be just as deadly as alcohol-impaired driving. Meanwhile, driving under the influence of drugs is becoming increasingly common across the United States.

Yet public awareness and policy responses continue to lag behind.

I study the prevalence and risk factors of drugged driving. Although public health messaging in the U.S. has long emphasized the dangers of alcohol-impaired driving, far less attention has been paid to the risks posed by other substances; even as drug-impaired driving becomes more widespread and complex.

Whether the substance is illegal, such as methamphetamine, or legal but still impairing — including cannabis, sedating sleep aids or certain prescription drugs like benzodiazepines and pain killers — the result is the same: impaired judgment, dulled reflexes and devastating outcomes on the road.

A different form of impairment: In 2020, an estimated 12.6 million people ages 16 and up drove after using illicit drugs. Of that total, roughly 11.7 million were under the influence of cannabis. In 2018, some 2.3 million people in the United States reported driving under the influence of illicit drugs other than marijuana during the previous 12 months. Globally, roadside surveys worldwide find that between 3.9 percent and 20 percent of drivers tested positive for drugs.

While alcohol typically impairs coordination and reaction time, drugs present a more complex picture. Cannabis, for example, slows reaction time and affects spatial awareness. Opioids can cause drowsiness and dizziness. Stimulants like cocaine or methamphetamine may lead to overconfidence and aggressive driving. When drugs are mixed — or combined with alcohol — the risks increase dramatically.

Cannabis, in particular, presents a unique challenge: It’s the most commonly used federally illegal drug in the United States, and public perception often downplays its risks behind the wheel.

Research from the AAA Foundation for Traffic Safety reveals that over 80 percent of cannabis users admit to driving just hours after using the drug, and nearly 20 percent believe their driving got much better. Multiple studies have found that drivers with THC, the primary psychoactive compound in cannabis, in their bloodstream are about twice as likely to be involved in a fatal crash — either as the cause or as a victim — compared with those who haven’t used drugs or alcohol. For alcohol, with a blood alcohol content of 0.08 percent, the odds of dying in a motor vehicle crash are approximately 13 times higher than sober drivers.

Outdated laws and patchy enforcement: Every U.S. state has laws prohibiting drug-impaired driving, but enforcement varies dramatically.

Some states, such as Texas and California, use “impairment-based” laws, which rely on observable signs of impairment. Others, such as Ohio, Wisconsin and Washington state, use per se laws, setting thresholds for drugs like THC — such as 5 nanograms per milliliter of blood.

Then there are zero-tolerance laws, in states like Georgia and Rhode Island, which penalize drivers for having any trace of a controlled substance while behind the wheel, regardless of whether they’re impaired at the time.

These inconsistencies create legal gray areas in how the laws are interpreted and enforced. For instance, in Illinois, it is a crime to drive with any trace of a controlled substance in your system, even if you are not impaired; and even if the drug was legally prescribed. In Arizona, medical cannabis patients cannot be convicted solely based on THC presence, but prosecutors can still argue impairment.

Detection is the biggest hurdle: A significant factor in the inconsistency from state to state is that there is no standardized way to measure drug impairment as there is with blood alcohol content.

While alcohol can be tested on the spot using a breathalyzer, detecting drug use is far more complicated. THC and other substances can linger in the body long after their impairing effects have worn off. Meanwhile, newer synthetic drugs such as spice or bath salts may not be detected at all without specialized equipment.

To address this, many states are turning to oral fluid testing — or saliva tests — which can detect recent drug use more quickly. As of late 2023, 27 states had authorized some form of roadside oral fluid screening.

Public misconceptions and potential solutions: Unlike alcohol, where there’s a clear legal limit of 0.08 percent blood alcohol concentration, there’s no easy-to-understand number for cannabis. Laws around driving after cannabis use vary widely and can be confusing. Scientists are still figuring out how much THC it takes to affect a person’s driving skills and to what degree, so it stands to reason that people don’t know how to judge it for themselves.

Another twist is that the roadside tests that cops use to spot drunk drivers don’t work as well for drug impairment. THC can linger in the body long after the high fades, so a test might not tell the whole story. New testing tools, like saliva swabs and eye-tracking, are being developed, but are not yet ready for application in real-life scenarios.

So what can you do? The big takeaway is that if you feel “different,” you’re probably driving differently, too. The National Highway Traffic Safety Administration’s “If You Feel Different, You Drive Different” campaign is a helpful reminder that even if you think you’re fine, your driving might not be.

If you’re riding with friends, don’t be shy about speaking up if someone looks or behaves as if they are impaired. Planning ahead with a designated driver or ride-share can make all the difference.

At the end of the day, it’s about making smart, safer choices; and being honest with ourselves and each other about what it really means to be safe on the road.

Andrew Yockey is an assistant professor of public health at the University of Mississippi. This article is republished from The Conversation under a Creative Commons license.