A 2008 study, taken from the Annals of Internal Medicine, suggest that some antihistamines may impair driving ability, even more than alcohol. The driver doesn’t even have to feel drowsy.
Forty study participants, when given diphenhydramine and an amount of alcohol to boost their blood alcohol level to .10 (legally impaired in most states), tested worse in a driving simulator when under the influence of antihistamine than under the influence of alcohol. A newer non-sedating antihistamine, Allegra, did not affect driving any more than the placebo given in a blind test screen.
The Asthma and Allergy Foundation of America estimates there are 50 million allergy sufferers in the United States. Allergies account for more than 17 million outpatient physician visits each year. Since the 1940s, antihistamines have been among the most widely prescribed medications. It is estimated that currently there are 30 million patients in the United State taking regular antihistamine medications in this $8 billion drug market.
If you have taken antihistamines, ask your doctor if a non-sedative prescription will work for you.