Use of illicit* drugs or misuse of prescription drugs can make driving a car unsafe—just like
driving after drinking alcohol. Drugged driving puts the driver, passengers, and others who
share the road at risk.
Why is drugged driving dangerous?
The effects of specific drugs differ depending on how they act in the brain. For example,
marijuana can slow reaction time, impair judgment of time and distance, and decrease
coordination. Drivers who have used cocaine or methamphetamine can be aggressive and
reckless when driving. Certain kinds of sedatives, called benzodiazepines, can cause dizziness
and drowsiness.
All of these impairments can lead to vehicle crashes.
Research studies have shown negative effects of marijuana on drivers, including an increase in crashes. Which drugs are linked to drugged driving?
After alcohol, marijuana is the drug most often found in the blood of drivers involved in
crashes.
Tests for detecting marijuana in drivers measure the level of delta9
tetrahydrocannabinol (THC), marijuana’s mindaltering ingredient, in the blood. But the role
that marijuana plays in crashes is often unclear. THC can be detected in body fluids for days or
even weeks after use, and it is often combined with alcohol. The risk associated with marijuana
in combination with alcohol, cocaine, or benzodiazepines appears to be greater than that for
either drug by itself.
Several studies have shown that drivers with THC in their blood were roughly twice as likely to
be responsible for a deadly crash or be killed than drivers who hadn't used drugs or alcohol.
However, a large NHTSA study found no significant increased crash risk traceable to marijuana
after controlling for drivers’ age, gender, race, and presence of alcohol. More research is
needed.
Along with marijuana, prescription drugs are also commonly linked to drugged driving crashes.
A 2010 nationwide study of deadly crashes found that about 47 percent of drivers who tested
positive for drugs had used a prescription drug, compared to 37 percent of those had used
marijuana and about 10 percent of those who had used cocaine. The most common prescription
drugs found were pain relievers. However, the study didn't distinguish between medicallysupervised
and illicit use of the prescription drugs.
How often does drugged driving cause crashes?
It's hard to measure how many crashes are caused by drugged driving. This is because:
a good roadside test for drug levels in the body doesn't yet exist
police don't usually test for drugs if drivers have reached an illegal blood alcohol level
because there's already enough evidence for a DUI charge
many drivers who cause crashes are found to have both drugs and alcohol or more than one
drug in their system, making it hard to know which substance had the greater effect.
One NHTSA study found that in 2009, 18 percent of drivers killed in a crash tested positive for
at least one drug. A 2010 study showed that 11 percent of deadly crashes involved a
drugged driver.
Why is drugged driving a problem in teens and young
adults?
Teen drivers are less experienced and are more likely than older drivers to underestimate or not
recognize dangerous situations. They are also more likely to speed and allow less distance
between vehicles. When lack of driving experience is combined with drug use, the results can
be tragic. Car crashes are the leading cause of death among young people aged 16 to 19
years.
A 2011 survey of middle and high school students showed that, in the 2 weeks before the
survey, 12 percent of high school seniors had driven after using marijuana, compared to around 10. Drugged Driving in Older Adults
In 2010, more than onequarter of drugged drivers in deadly crashes were aged 50 years or
older.
Illicit drug use in adults aged 50 to 59 has increased, more than doubling from 3 percent in 2002
to 7 percent in 2010.
Mental decline in older adults can lead to taking a prescription drug more or less often than they
should or in the wrong amount. Older adults also may not break down the drug in their system as
quickly as younger people. These factors can lead to unintended intoxication while behind the
wheel of a car.
A study of college students with access to a car found that 1 in 6 had driven under the
influence of a drug other than alcohol at least once in the past year. Marijuana was the most
common drug used, followed by cocaine and prescription pain relievers.
What steps can people take to prevent drugged driving?
Because drugged driving puts people at a higher risk for crashes, public health experts urge
people who use drugs and alcohol to develop social strategies to prevent them from getting
behind the wheel of a car while impaired. Steps people can take include:
offering to be a designated driver
appointing a designated driver to take all car keys
getting a ride to and from parties where there are drugs and alcohol
discussing the risks of drugged driving with friends in advance
In 2014, 10 million people aged 12 or older reported driving under the influence of illicit drugs in
the past year.
It's hard to measure how many crashes drugged driving causes.
After alcohol, marijuana is the drug most often linked to drugged driving.
In 2010, more than onequarter of drugged drivers in fatal crashes were aged 50 years or older.
When lack of driving experience is combined with drug use, the results can be tragic.
People who use drugs and alcohol should develop social strategies to prevent them from getting
behind the wheel of a car while impaired.
Source: National Institute on Drug Abuse.