Along with spring-like weather comes the inevitable hay-fever season, and a recent study has found that over-the-counter medications used to combat allergies may impair driving ability more than alcohol.

The study, conducted at the University of Iowa and published in Tuesday’s issue of Annals of Internal Medicine, found that a standard dose of the antihistamine used in medicines such as Benadryl had a more significant effect than alcohol on drivers.

During the study, 40 allergy sufferers reported once a week over a four-week period to a driving simulator in Iowa City. Each participant was given a standard dose of the antihistamine known as diphenhydramine.

The study indicated diphenhydramine impaired subjects’ ability to steer a vehicle, avoid crossing into an oncoming lane and match the speed of a vehicle ahead more than subjects who drove the same simulator while drunk.

John Aagesen, pharmacist at Hy-Vee Pharmacy Clinic, 3600 West Lincoln Way, said over-the-counter antihistamines have long been known to cause drowsiness.

“I don’t know anything about antihistamines affecting you like you’re drunk,” he said, “but I do know that most over-the-counter antihistamines can make you feel drowsy.”

Tim Cmelik, manager at the Student Health Center Pharmacy, said he had not reviewed the study himself, but agreed with Aagesen, saying antihistamines often cause side effects, including drowsiness.

However, he noted over-the-counter antihistamines do not have the same effect on all people.

“Everyone’s body makeup is different,” he explained. “Some people just aren’t affected by [over-the-counter] antihistamines.”

Researchers conducting the study also looked at fexofenadine, which is also used in prescription hay fever medications, most notably Allegra. Fexofenadine seemed to have no effect on driving ability.

Aagesen said prescription antihistamines with fexofenadine do not normally cause drowsiness.

“Non-sedating antihistamines like Allegra generally do not carry the same side effects as over-the-counter antihistamines,” he said.

Still, the U of I study has come under fire from Warner-Lambert Co., the manufacturer of Benadryl. The company said the study is “seriously flawed” because it was partially funded by Aventis, the maker of Allegra.

John M. Weiler, professor of internal medicine at U of I and one of the study’s investigators, denied Warner-Lambert’s accusation, saying he was “not for sale.”

But whether it’s Benadryl or Allegra, Cmelik and Aagesen said they alert people who use prescription and over-the-counter hay fever medications about the potential side effects.

“I always caution people to be careful when driving or operating machinery if they’re using an antihistamine,” Aagesen said.

The Associated Press contributed to this story.