FTA Drug and Alcohol Regulation Updates
Issue 29, page 5

Antihistamines Impair Driving
Since the late 1980ís, the National Transportation Safety Board (NTSB) has investigated numerous accidents caused in part by the standard use of over-the-counter (OTC) medications. Sedating antihistamines obtained over-the-counter contributed to a large number of these accidents.
   Antihistamines can cause drowsiness, impaired coordination, inability to concentrate and dizziness. Medical research has found that the antihistamine diphenhydramine, found in Benadryl, Tylenol Severe Allergy, and Sominex, actually causes greater impairment than alcohol. University of Iowa researchers found that the standard dose of antihistamine contained in Benadryl and similar medicines had a greater effect than a few drinks on a driverís ability to match the speed of the vehicle ahead, adversely effected steering stability and increased the likelihood of crossing into the oncoming lanes1.
   The researchers tested performance using a driving simulator to test participantsí abilities once after taking diphenhydramine, once using a non-drowsy antihistamine (fexofenadine found in Allegra), once with a placebo and once when the participant had a blood-alcohol concentration of 0.1 percent. The participantsí impairment, as evidenced by following and steering abilities, was significantly worse after the participants took diphenhydramine than when they took alcohol. The number of times the participants crossed into the oncoming lane was twice as great after taking diphenhydramine as after taking fexofenadine or the placebo. Researchers also determined that the participantsí assessments of how drowsy they were did not correlate with their performance, suggesting that people who take antihistamines may not be able to judge when they are impaired, further adding to the risk.
   Antihistamines are used by millions of Americans that suffer from hay fever and allergies. Most of these medications come with warning labels cautioning that they may cause drowsiness and should not be used while operating heavy machinery. There are also warnings about mixing antihistamines with alcohol. Unfortunately, people often donít read or ignore the warnings.
   Several European countries require drug manufacturers to color-code their packages with symbols that indicate which drugs may cause drowsiness or impair a personís ability to drive or operate heavy machinery safely. The National Transportation Safety Board has recommended that the FDA establish a similar labeling requirement for over-the-counter drugs.
   In the mean time, employers must educate employees regarding the dangers associated with the use of over-the-counter medications, especially antihistamines that cause drowsiness. Employees should be taught how to read labels, how to talk to physicians and pharmacists, how to be aware and recognize side effects, and how to tell their supervisors if they feel impaired as a result of medications, lack of sleep or other causes.
   Allergy and hay fever sufferers have non-drowsy, antihistamine alternatives (e.g., Claritin, Allegra and Zyrtec). Claritin, once available only by prescription, is now available over-the-counter. Many individuals, however, are not aware of the difference between sedating and non-sedating antihistamines and may use them interchangeably. The over-the-counter forms are easiest to obtain since they do not require a prescription, but typically cause performance impairment (except for Claritin), while the prescription alternatives typically do not impair performance, but are more difficult to obtain. Employees should speak with their health care provider or pharmacist about the potential side effects of medications and should seek out non-drowsy alternatives if possible.
   The FTA strongly encourages transit systems to directly notify safety-sensitive employees regarding the dangers of sedating antihistamine use and other over-the-counter and prescription medications through training, brochures, notices, or other means of communication that have proven effective.

1Weiler, John M., Effects of Fexofenadine, Diphenhydramine, and Alcohol on Driving Performance, Annals of Internal Medicine, March 7, 2000, Volume 132, Issue 5, pages 354-363.

Where to Find? .....

Conforming Products List
Evidential Breath Testing (EBT) Devices
July 21, 2000
Federal Register Vol.65
Pages 45419 - 45423
Primary Topic: Conforming Products List (CPL)
Website location: www.nhtsa.gov/

Note: This list will be updated periodically.

Non-evidential Testing Devices
May 4, 2001
Federal Register Vol.66
Pages 22639 - 22640
Primary Topic: Initial Alcohol Screening Devices

Note: This list will be updated periodically.

FTA Drug & Alcohol Discussion Forum:

Drug and Alcohol Audit Questions





The information presented on this page should be used to update Chapter 5 of the revised Implementation Guidelines.

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