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Which Popular Drugs Make People Dangerous Behind the Wheel?

Who would guess that a common over-the-counter medicine could affect driving even more than alcohol? Law-abiding citizens who would never dream of drinking and driving could be a hazard on the highways during the upcoming allergy season.

One of the best selling nonprescription antihistamines is diphenhydramine (DPH). It is found in products such as Benadryl, Dramamine, Excedrin P.M., Nytol and Tylenol PM. A study in the Annals of Internal Medicine (March 7, 2000) concluded that “diphenhydramine had a greater impact on driving than alcohol did.”

The scientists used a state-of-the-art driving simulator to test drivers’ ability to maintain a constant distance from the car ahead, steer safely, stay in the lane and avoid collisions. Prior to the driving test, subjects were given enough alcohol to reach 0.1 percent blood alcohol (legally drunk), 50 mg of DPH, 60 mg of fexofenadine (Allegra) or placebo pills.

Unfortunately, drowsiness was not a reliable indicator of driving impairment. The drivers were asked to rate their drowsiness, but some people who felt wide awake performed very poorly. According to the researchers, “This suggests that drivers who use alcohol or diphenhydramine are probably mistaken if they believe that lack of drowsiness means that they will be able to drive without impairment.”

This is bad news for anyone who takes medicine and gets behind the wheel of a car. Most warnings about driving impairment assume that a person will be able to judge how much he is affected. The label for Benadryl states, for example: “marked drowsiness may occur…be careful when driving a motor vehicle or operating machinery.”

Aside from the frightening implication that one might not always be careful when driving, such a label is not very helpful. In our opinion, medicines containing diphenhydramine should be clearly labeled “Do not drive after taking this drug.” The new research suggests that people on such medications may be at least as dangerous as drunk drivers but without realizing it.

Hundreds of other over-the-counter and prescription medications have inadequate precautions on the label. Products such as cold and allergy medicines, cough suppressants, antidepressants and anti-anxiety agents may also impair motor coordination, judgment or reaction time.

The FDA has acknowledged that several popular sleeping pills may linger in the body during morning hours. Last year the agency issued the following safety announcement:

“The U.S. Food and Drug Administration (FDA) is notifying the public of new information about zolpidem [Ambien], a widely prescribed insomnia drug. FDA recommends that the bedtime dose be lowered because new data show that blood levels in some patients may be high enough the morning after use to impair activities that require alertness, including driving…

“FDA is also reminding the public that all drugs taken for insomnia can impair driving and activities that require alertness the morning after use. Drowsiness is already listed as a common side effect in the drug labels of all insomnia drugs, along with warnings that patients may still feel drowsy the day after taking these products. Patients who take insomnia drugs can experience impairment of mental alertness the morning after use, even if they feel fully awake.”

Last spring, the FDA added a new warning about Lunesta (eszopiclone):

“The U.S. Food and Drug Administration (FDA) is warning that the insomnia drug Lunesta (eszopiclone) can cause next-day impairment of driving and other activities that require alertness…”

“A study of Lunesta found that the previously recommended dose of 3 mg can cause impairment to driving skills, memory, and coordination that can last more than 11 hours after receiving an evening dose.  Despite these driving and other problems, patients were often unaware they were impaired.  The new lower recommended starting dose of 1 mg at bedtime will result in less drug in the blood the next day.”  

For the most part both OTC and prescription drug labels carry meaningless platitudes to “use caution when driving.” Some suggest that people can assess their level of impairment and determine whether or not the drug has affected their ability to drive or operate machinery. This is a little like asking someone who has had three or four cocktails to determine her judgment and reaction time and use caution when driving home.

People who depend on their cars to get to work or do errands can’t always avoid driving because of an allergy medicine, a sleeping pill or an antidepressant. But we now know that they may not be able to evaluate their safety behind the wheel. If you must drive, ask your doctor for medications that won’t make you a hazard on the highway.

There is a wealth of information about non-sedating ways to control allergy symptoms this fall in our book, Best Choices from The People’s Pharmacy.

Even if you are not taking such medications, millions of other people are. That is especially true in the upcoming weeks when allergy season is at its peak. So, be extra careful to watch out for impaired drivers. They may not realize how dangerous they really are to themselves or you.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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