How do drugs affect driving?

Whether prescription, over the counter or illegal drugs, they can impair driving skills including vision, reaction time, judgment, hearing, and simultaneous task processing/accomplishments. Driving requires other cognitive skills such as information processing and psychomotor skills, which may also be impaired by the use of drugs. When drugs are mixed with alcohol, the results can be devastating.

Alcohol alters the mind, affects thinking, judgment, slows reaction time and interferes with coordination. Tasks requiring divided attention are most sensitive to alcohol effects. The more a person drinks the more likely that person is to drive. Alcohol and other drug involvement are much more likely in nighttime crashes.

Marijuana is also mind altering. Thinking and reflexes are slowed, causing difficulty in responding to sudden unexpected events. A driver’s ability to “track” or stay in his lane, to brake quickly, and to maintain the correct distance between cars is affected. Cocaine is a brain stimulant that causes anxiety, delusions, seizures, and lack of concentration, memory problems and blackouts. There is an increase in impulsive behavior with tendencies to take more risks and create confusion within the user. A person using cocaine maintains the illusions of being alert and stimulated although physical reactions are impaired.

The most dramatic effects of cocaine and driving are on vision. Cocaine may cause higher sensitively to light, halos around bright objects, and difficulty focusing.

Tranquilizers and Barbiturates are particularly dangerous in conjunction with alcohol because the mixture increases the accident risk beyond that found with anyone on drugs alone. Particularly strong is the interaction between alcohol and diazepam (Valium).

Over the counter medications Alcohol can enhance some of the dangerous side effects of the medications so to make driving dangerous. Most drugs for colds, hay fever, allergy, or to calm nerves can make a person drowsy when alcohol is consumed.

With stimulant-based drugs, a driver would actually feel that they were a better driver while they were under its influence, but they would become much more likely to drive recklessly and dangerously.
With depressant-based drugs, the driver would lose any real anxiety about the dangers on the road and would not be able to react quickly to changing driving conditions.
With hallucinogenic drugs reaction time will be altered and the driver’s ability to operate the vehicle will become erratic.

Information on this section was derived from the following websites

Study: Prescription Drugs Clouding Drivers

Drivers who test positive for drugs are more likely to use prescription drugs and to take multiple drugs at once. Read the full article:

  • Conservative estimates show that 20% of crashes in the U.S. are caused by drugged driving. This translates into about 6,761 deaths, 440,000 injuries and $59.9 billion in costs each year.
  • In a national survey, drugs were present more than 7 times as frequently as alcohol among weekend nighttime drivers in the U.S., with 16% testing positive for drugs, compared to 2% testing at or above the legal limit for alcohol.
  • Effective drugged driving prevention is one of the best ways to improve highway safety, to reduce illegal drug use and to get more drug abusers into addiction treatment.

This website has a lot of good information on drugged driving

Drugged driving is on the scale of drunk driving

On the nation's highways, drugged driving now poses a danger on the scale of the better-known problem of drunk driving. In a national survey, drugs were present more than 7 times as frequently as alcohol among weekend nighttime drivers in the U.S., with 16% testing positive for drugs, compared to 2% testing at or above the legal limit for alcohol. In addition, a recent study of seriously injured drivers at the Maryland Shock Trauma Center showed that 5l% of the sample tested positive for illegal drugs, compared to 34% who tested positive for alcohol In 2007, nearly 10 million people drove under the influence of drugs



Young drivers are particularly at risk for being impacted by drugged driving as supported by data on youth behaviors. Monitoring the Future showed that 30% of high school seniors had driven impaired or had been a passenger of an impaired driver in the two weeks prior to being surveyed. Nearly one quarter (23.2%) of high school seniors said they drove or rode with a driver after he or she used marijuana while 15.8% said they drove or


Which drugs do drugged drivers use?

In a study of seriously injured drivers, 26.9% tested positive for marijuana while 11.6% tested positive for cocaine, and 5.6% tested positive for either methamphetamine or amphetamine. These percentages are far higher than those detected among drivers in the 2007 NHTSA National Roadside Survey (NRS) which found 8.6% of weekend nighttime drivers positive for marijuana, 3.9% positive for cocaine, and 1.3% positive for methamphetamine. The higher statistics from the crash study compared to the NRS random driver sample are clear evidence that drugged driving is a serious threat to highway safety.
Additionally, in a recent British Columbia roadside study of drivers, 10.4% of drivers who provided an oral fluid sample tested positive for at least one drug other than alcohol. Cannabis and cocaine were the most commonly detected illegal substances, with 4.6% of drivers testing positive for each. 0.9% of drivers tested positive for opiates. Amphetamines, methamphetamine and benzodiazepines were detected in less than 1% of drivers.
Of the total number of positive drug tests, cannabis accounted for 49.4%. Cocaine was detected in 29.3% of positive cases while opiates were detected in 14.8%. Cannabis and cocaine was the most common polydrug combination, and accounted for 8.3% of all positive drug cases.
Taken from website Stop Drugged Driving

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