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 medications. More than 11 percent tested positive for illicit drugs. Another NHTSA study found that in 2009, among fatally injured drivers, 18 percent tested positive for at least one drug (e.g., illicit, prescription, or over-the-counter), an increase from 13 percent in 2005. (repeated below).

What Is Drugged Driving?

“Have one [drink] for the road” was once a commonly used phrase in American culture. It has only been within the past 25 years that as a Nation, we have begun to recognize the dangers associated with drunk driving. And through a multipronged and concerted effort involving many stakeholders—including educators, media, legislators, law enforcement, and community organizations such as Mothers Against Drunk Driving—the Nation has seen a decline in the numbers of people killed or injured as a result of drunk driving. But it is now time that we recognize and address the similar dangers that can occur with drugged driving.

The principal concern regarding drugged driving is that driving under the influence of any drug that acts on the brain could impair one’s motor skills, reaction time, and judgment. Drugged driving is a public health concern because it puts not only the driver at risk but also passengers and others who share the road.

However, despite the knowledge about a drug’s potentially lethal effects on driving performance and other concerns that have been acknowledged by some public health officials, policy officials, and constituent groups, drugged driving laws have lagged behind alcohol-related driving legislation, in part because of limitations in the current technology for determining drug levels and resulting impairment. For alcohol, detection of its blood concentration (BAC) is relatively simple, and concentrations greater than 0.08 percent have been shown to impair driving performance; thus, 0.08 percent is the legal limit in this country. But for illicit drugs, there is no agreed-upon limit for which impairment has been reliably demonstrated. Furthermore, determining current drug levels can be difficult, since some drugs linger in the body for a period of days or weeks after initial ingestion.

How Many People Take Drugs and Drive?

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 medications. More than 11 percent tested positive for illicit drugs.1 Another NHTSA study found that in 2009, among fatally injured drivers, 18 percent tested positive for at least one drug (e.g., illicit, prescription, or over-the-counter), an increase from 13 percent in 2005.2 Together, these indicators are a sign that continued substance abuse education, prevention, and law enforcement efforts are critical to public health and safety.

According to the 2009 National Survey on Drug Use and Health (NSDUH), an estimated 10.5 million people aged 12 or older reported driving under the influence of illicit drugs during the year prior to being surveyed.3 This corresponds to 4.2 percent of the population aged 12 or older, similar to the rate in 2008 (4 percent) and not significantly different from the rate in 2002 (4.7 percent). (Judge’s Comment: Using 12 and older is rather odd as we would hope there would be very few drivers between the age of 12 and 16. I believe this skews the figures and would actually cause the percentage between the ages of 16 and 25 to significantly increase.) In 2009, the rate was highest among young adults aged 18 to 25 (12.8 percent). In addition, NSDUH reported the following:

• In 2009, an estimated 12 percent of persons aged 12 or older (30.2 million persons) drove under the influence of alcohol at least once in the past year. This percentage has dropped since 2002, when it was 14.2 percent.

• Driving under the influence of an illicit drug or alcohol was associated with age. In 2009, an estimated 6.3 percent of youth aged 16 or 17 drove under the influence. This percentage steadily increased with age to reach a peak of 24.8 percent among young adults aged 21 to 25(emphasis added). Beyond the age of 25, these rates showed a general decline with increasing age.

• Also in 2009, among persons aged 12 or older, males were more likely than females (16.9 percent versus 9.2 percent, respectively) to drive under the influence of an illicit drug or alcohol in the past year.

Results from NIDA’s Monitoring the Future survey indicate that in 2007, more than 12 percent of high school seniors admitted to driving under the influence of marijuana in the 2 weeks prior to the survey.

How do Drugs Affect Driving?

Drugs – whether prescription, over-the-counter or illegal drugs – can impair necessary driving skills including vision, reaction time, judgment, hearing, and simultaneous task processing/accomplishment. 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.

• Marijuana:  Marijuana has been linked to the impairment of the ability to drive a vehicle. Concentration is affected and there is difficulty in perceiving time and distance, which can lead to the following: bad judgment, impaired reaction time, poor speed control, an inability to accurately read signs, drowsiness, and distraction. When marijuana is combined with alcohol it creates greater impairment in areas such as reaction time and coordination.

When combined with sedatives and opiates, it can cause an increase in anxiety and even hallucinations, along with an increase in heart rate and blood pressure when used with amphetamines. On the other hand, effects are somewhat unpredictable when marijuana is combined with stimulants, such as nicotine, caffeine, amphetamines, and cocaine.

• Cocaine: Cocaine may successfully mask fatigue; however, high dosages impair judgment and interfere with the ability of the driver to concentrate. Coordination and vision are impaired. There is an increase in impulsive behaviors with tendencies to take more risks and create confusion within the user. A person using cocaine maintains the illusion of being alert and stimulated, although physical reactions are impaired.

Additive effects are noted when cocaine is combined with over-the-counter products, such as diet pills or antihistamines. Cocaine taken with psychotropic drugs, especially antidepressants, can be extremely detrimental.  A person who has extremely high blood pressure and uses cocaine may suffer from a stroke or heart attack.

Some users combine cocaine with alcohol and sedatives to cushion the "crash" or feeling of depression and agitation that sometimes occurs as the effects of cocaine wear off. Further research indicates that additive and antagonistic effects can be produced when cocaine is mixed with alcohol.

If cocaine is used in high doses, as in the case of overdose, alcohol will probably have an additive effect on the symptoms that eventually contribute to death.

When cocaine is injected in combination with heroin, sometimes called "speedballing," there is an increased risk of toxicity, overdose, and death.

• Tranquilizers: The use of tranquilizers produces drowsiness, a lack of coordination, altered perceptions, memory impairment, poor control of speech, and slower reaction time. Effects on driving include poor tracking, difficulty in maintaining lane position, and neglecting roadside instructions.

Some people in methadone treatment programs use benzodiazepines to enhance the effects of methadone. When tranquilizers are combined with alcohol or other central nervous system depressants, synergistic effects may be produced, which may be fatal. Alcohol increases the absorption of benzodiazepines, slows their break down in the liver and can cause cardiovascular and respiratory depression. People who take stimulants sometimes take tranquilizers to off set agitation and sleepiness.

• Opiates: Opiates can cause drowsiness, mental confusion, and visual impairment even at lower, moderate doses. A driver may have difficulty keeping the vehicle in the correct lane and may make errors in judgment.

Alcohol greatly increases the present effects of opiates and can lead to respiratory arrest. A person injecting heroin mixed with cocaine or methamphetamines, known as "speedballing," produces a stimulant effect. The listed drug combinations increase the risk of toxicity, overdose, and death.

• Amphetamines: The use of amphetamines can interfere with concentration, impair vision, and increase the driver's tendencies to take risks. Amphetamines should never be taken with a class of antidepressants known as MAO inhibitors, because of potential hypertensive crisis.

Amphetamine users sometimes use marijuana and depressant drugs in order to avoid the adverse side effects of the "crash," therefore creating multiple drug dependencies.

Drug combinations (called poly-drug use) may cause one of three reactions: additive, synergistic or antagonistic.