Addict Help

Addiction Info Center

Home News OTC Antihistamines Could Cause Impaired Driving

OTC Antihistamines Could Cause Impaired Driving


Fall allergy season is still officially underway and, if you didn’t know already, ragweed is the biggest culprit going into the early winter months. With a little bit of luck, a late October, early November cold-snap will knock it out of the air.

Allergies are the sixth leading cause of chronic illness in the U.S. and to get relief, millions of busy Americans reach for over-the-counter (OTC) antihistamines containing Diphenhydramine (Benadryl®) so they can continue to function.

  • This, however, presents a problem, because even over-the-counter antihistamines contain enough sedatives to impair a person, especially when they’re behind the wheel.

Impaired Driving

DWAI stands for “Driving Whiling Ability Impaired”.

“One 50-milligram dose containing Diphenhydramine (Benadryl® et al) has the same effect on driving performance as 6 to 8 ounces of alcohol,” Dr. Gary Lulenski, an ear, nose and throat specialist in St. Joseph, Michigan, told The Herald Palladium. “Its effect is greater than a .10 blood alcohol level.”

Also, according to the Florida Department of Transportation, multiple studies have indicated antihistamines have been shown to cause impaired driving issues. To quote from it “The participants’ 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 participants’ 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.”

The University of Kansas research also indicated Diphenhydramine seriously effected operating an automobile.

“For example, separate studies from the University of Iowa and Minnesota found that driver impairment caused by (first-generation) Benadryl was similar to impairment caused by significant amounts of alcohol. Further, the Iowa study found that drivers taking Benadryl could not accurately judge its effect on their driving.”

“First generation antihistamines, such as diphenhydramine, are known to affect driving performance,” said the study’s lead author, Dr. John Weiler, a professor of medicine at the university. “However, we were surprised to find that this antihistamine has more impact on driving performance than alcohol does.”

  • The Iowa study also confirmed that drivers intoxicated on diphenhydramine (Benadryl) are less likely to realize they were impaired. Participants appeared unable to accurately assess their poor motor skills.

Even with all the available evidence that driving “drunk” on Diphenhydramine is dangerous and illegal, there’s little public awareness because the medication is over-the-counter. It’s important to always read the warning labels on medications, prescription or otherwise, and avoid putting yourself or anyone else at risk of injury or death.

Lawyer’s Warning

In this CA lawyer’s blog, “What most California drivers do not know is that it is possible to be arrested and charged with driving under the influence (DUI) of Benadryl. Yes, under California law if an officer has probable cause to believe that your driving was impaired and you test positive for any amount of a drug that could affect your ability to drive —whether it is illegal, prescription, or over-the-counter—you can and probably will be charged with driving under the influence of a drug.”

Simulator Testing

Even the National Institute of Health study reached similar conclusions;

“…After participants took diphenhydramine, driving performance was poorest, indicating that diphenhydramine had a greater impact on driving than alcohol did. Drowsiness ratings were not a good predictor of impairment, suggesting that drivers cannot use drowsiness to indicate when they should not drive.”

The side effects of antihistamine medications containing Diphenhydramine (Benadryl®) Chlor Trimeton and others) are listed on the packaging, but because many of these meds are over-the-counter, people assume they’re safe to consume and drive. Unfortunately, that’s not always case.

Side effects on some antihistamines can include the following:

  • Shortened attention span
  • Poor coordination and feeling “foggy”
  • Drowsiness
  • Fatigue

NTB Warning

“Sedating antihistamines obtained over-the-counter have contributed to a large number of [car] accidents,” reports the National Transportation Safety Board (NTSB). The agency, whose mission is to formulate transportation policies that keep Americans safe, has tracked the effects of over-the-counter medications on drivers since the 1980s and is well aware how dangerous it is for people to drive “drunk” on these seemingly safe OTC medications.


A study conducted at the University of Iowa documented the effects of antihistamines on drivers. Participants were given diphenhydramine, the active ingredient in hay-fever medications (like Tylenol Severe Allergy, fexofenadine, found in Allegra, alcohol) or a placebo. They then got behind the wheel in a driving simulator.

They had difficulty matching the speed of vehicles in front of them, had unstable steering coordination and were more likely to cross into oncoming lanes.

Second Generation Antihistamines

Participants given fexofenadine, which is a second-generation antihistamine, alcohol or the placebo faired much better in the driving simulator.

Even as allergy season comes to a close in the early winter months, cold and flu season kicks off. So remember to never drive while under the influence of Diphenhydramine or any other sedative antihistamines.

Pin It on Pinterest

Share This

Share this post with your friends!