Use of any psychoactive (mind-altering) drug makes it highly unsafe to drive a car and is illegal—just like driving after drinking alcohol. Drugged driving puts at risk not only the driver but also passengers and others who share the road. ~National Institute on Drug Abuse

Why Is Drugged Driving Hazardous?

The effects of specific drugs of abuse differ depending on how they act in the brain, but all impair faculties necessary for the safe operation of a vehicle. These faculties include motor skills, balance and coordination, perception, attention, reaction time, and judgment. Even small amounts of some drugs can have a measurable effect on driving ability.

How Many People Take Drugs and Drive?

According to the 2012 National Survey on Drug Use and Health (NSDUH), an estimated 10.3 million people aged 12 or older (or 3.9 percent of adolescents and adults) reported driving under the influence of illicit drugs during the year prior to being surveyed. This was higher than the rate in 2011 (3.7percent) and lower than the rate in 2002 (4.7 percent). By comparison, in 2012, an estimated 29.1 million persons (11.2 percent) reported driving under the influence of alcohol at least once in the past year. (This percentage has dropped since 2002, when it was 14.2 percent.)

According to the National Highway Traffic Safety Administration’s (NHTSA) 2007 National Roadside Survey, more than 16 percent of weekend, nighttime drivers tested positive for illegal, prescription, or over-the-counter drugs. More than 11 percent tested positive for illicit drugs.

According to NSDUH data, men are more likely than women to drive under the influence of an illicit drug or alcohol. And young adults aged 18 to 25 are more likely to drive after taking drugs than other age groups.

How Often Does Drugged Driving Cause Accidents?

It is hard to measure the exact contribution of drug intoxication to driving accidents, because blood tests for drugs other than alcohol are inconsistently performed, and many drivers who cause accidents are found to have both drugs and alcohol in their system, making it hard to determine which substance had the greater effect.

Teens and Drugged Driving

Vehicle accidents are the leading cause of death among young people aged 16 to 19. When teens’ relative lack of driving experience is combined with the use of marijuana or other substances that affect cognitive and motor abilities, the results can be tragic.

Between 2001 and 2006, 14.1 percent of high school seniors responding to the Monitoring the Future survey admitted to driving under the influence of marijuana in the 2 weeks prior to the survey.

One NHTSA study found that in 2009, 18 percent of fatally injured drivers tested positive for at least one illicit, prescription, or over-the-counter drug (an increase from 13 percent in 2005).

What Drugs Contribute to Accidents?

After alcohol, THC (delta-9-tetrahydrocannabinol), the active ingredient in marijuana, is the substance most commonly found in the blood of impaired drivers, fatally injured drivers, and motor vehicle crash victims. Studies in several localities have found that approximately 4 to 14 percent of drivers who sustained injury or died in traffic accidents tested positive for THC.

A study of over 3,000 fatally injured drivers in Australia showed that when THC was present in the blood of the driver, he or she was much more likely to be at fault for the accident. Additionally, the higher the THC concentration, the more likely the driver was to be culpable.

Considerable evidence from both real and simulated driving studies indicates that marijuana can negatively affect a driver’s attentiveness, perception of time and speed, and ability to draw on information obtained from past experiences. Research shows that impairment increases significantly when marijuana use is combined with alcohol.

Other drugs commonly implicated in accidents include opiates, amphetamines, benzodiazepines, and cocaine. For instance, in a 2003 study of seriously injured drivers admitted to a Maryland shock trauma center, drugs other than alcohol were present in more than half of the cases. These included marijuana (26.9 percent), cocaine (11.6 percent), benzodiazepines (11.2 percent), and opiates and other prescription drugs (10.2 percent). A quarter of the cases involved both alcohol and other drugs.

Many prescription drugs including opioid pain relievers and benzodiazapenes prescribed for anxiety or sleep disorders come with warnings against the operation of machinery—including motor vehicles—for a specified period of time after use. When prescription drugs are abused (taken without medical supervision), impaired driving and other harmful reactions become much more likely.