Driving a car while under the influence of drugs is very dangerous, as the intoxicating effects can impair driving judgment and ability. [1] Now, new research has shown that nearly half of fatal road traffic accidents are linked to drug use. [2]
Nearly half of fatal wrecks linked to illegal drugs
New research analyzed the records of deceased drivers from Montgomery County, Ohio, from 2019 to 2024. [2] Of the 246 drivers, they found that 41.9% had blood samples that tested positive for delta-9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis. [2] Cannabis was legalized in the state in 2023; however, this did not significantly increase the rate of drivers testing positive for THC. [2]
The average THC blood level in this study was 30.7 ng/ml, far above most legal limits of 2-5 ng/ml. [2] This signifies recent cannabis consumption before driving, and is enough to cause significant impairment to driving ability. [2]
Understanding the data: Methods, scope, and limitations
This study analyzed coroner records for road traffic fatalities and any associated drug use. However, they only looked at data about THC levels in fatal car accidents over six years from one county in Ohio. The study is therefore limited in terms of the type of substance analyzed, timeframe, and location. However, analysis of these coroner records has provided valuable data about the extent of cannabis involvement in fatal car accidents, data that is likely similar across other states.
How drug impairment increases crash risk & severity
A recent survey found that millions of people have driven a vehicle under the influence of drugs or alcohol. [1] Different drugs can affect driving ability in various ways, but they can all cause impairment and increase crash risk. [1] For example, cannabis can impair judgment, slow reaction time, and decrease coordination, whereas cocaine can lead to more aggressive and reckless driving. [1]
If multiple substances are taken together, including alcohol, driving ability can be even further impaired. [1] Drug impairment can increase the severity of crashes due to slower reaction times and impaired perception, which can reduce braking or evasive maneuvers, leading to more high-impact crashes.
Which drugs are most involved?
While this study found THC to be linked to over 40% of fatal car accidents, other studies have also linked other substances to these fatalities. Data from 1998-2010 across the U.S. found alcohol to be found in 45% of fatally injured drivers. [3] Stimulant substances and cannabinoids were the most commonly found drugs and were present at a similar frequency in this study. [3] Whereas, research from Australia found that methamphetamine was the most common illicit substance associated with road traffic fatalities. [4]
Single-vehicle crashes are more associated with alcohol use than with drug use. [3] Alcohol was also found to be much more prevalent in crashes on the weekend and at night, whereas drug prevalence was fairly consistent throughout the week and time of day. [3] A separate study also found that different substances were associated with different types of crashes and traffic violations, such as speeding or running red lights. [5]
The role of polydrug use
Using multiple substances together, either to enhance their effects or overcome unwanted side effects, is common. However, using multiple substances can lead to significant driving impairment. The combination of alcohol and cannabis was the most commonly seen in fatal car accidents. [6]
Alcohol and cannabis can affect driving in different ways. Alcohol impairs lane position, slows braking time, and reduces the ability to detect hazards, [7] whereas cannabis can affect time perception and cause drowsiness. [8] This synergistic effect creates a dangerous combination, which is reflected in the higher number of fatal accidents.
Public health and safety strategies
Drug-driving is a significant public health concern, as it puts the lives of the public at risk. Addressing drug-related driving required a combination of education, law enforcement, and policy interventions. The National Transportation Safety Board (NTSB) has published several recommendations to help combat this issue, including: [6]
- Labels on cannabis products that warn people not to drive after consumption.
- Ensure drug manufacturers have accurately evaluated the drug effects on the user’s ability to drive a motor vehicle.
- Stricter laws for those who are caught driving under the influence of drugs or alcohol.
Treatment and prevention programs are also crucial. Many drug-involved crashes involve individuals struggling with substance use disorders. Providing accessible treatment options and interventions that address the root causes of substance use can help reduce repeat offenses and save lives.
Challenges, ethical, & social considerations
Testing for drug impairment presents ethical concerns around privacy and accuracy. Unlike alcohol breath tests, drug testing typically requires blood or urine samples, which are more invasive. Additionally, some drugs can remain detectable in the body long after their impairing effects have worn off, raising questions about whether a positive test always indicates impairment at the time of driving. With cannabis legalization becoming more common, individuals must remember that, as with alcohol, while it might be legal to take cannabis, it’s not legal to drive impaired by it.
There are also equity concerns with regard to enforcement. Studies have shown that non-white communities are disproportionately targeted for traffic stops, which could then result in drug testing. [9] Ensuring that enforcement efforts are fair and do not perpetuate existing inequalities is an important consideration for law enforcement agencies.
What drivers can do to stay safe and compliant
Drivers must ensure they never drive while impaired by drugs or alcohol. If individuals need transportation while impaired, they should ensure they have a sober driver to take them, and not drive themselves. It’s important to remember you can still be impaired the next morning after a night of drinking or taking drugs.
Some prescription and over-the-counter medications can affect your driving, often by causing drowsiness or sedation. It’s important to recognize the signs of impairment in yourself and others. If you feel drowsy, dizzy, or have difficulty concentrating, it’s not safe for you to drive.
Final thought
Research has shown that drug-involved driving is a major contributor to fatal traffic accidents. As cannabis legalization expands and new psychoactive substances emerge, this public health crisis requires urgent attention.
Individuals should plan ahead and never get behind the wheel if impaired by drugs or alcohol. Driving sober helps to protect yourself, your passengers, and everyone else sharing the road with you. If you, or someone you know, is struggling with substance use, please reach out to a healthcare professional.
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