Why Are Antihistamines Found in Over the Counter Products?

Antihistamines, or "histamine antagonists," are drugs that bind and disable the body's histamines. Histamines are molecules produced by cells in the body that signal the presence of foreign viruses and bacteria as well as pollen, dander and other causes of allergic reaction. They are present in over-the-counter medicines because they can stop the effects of allergies or symptoms of disease like sneezing, runny nose, coughing and red, itchy eyes.

Biological Response

• When viruses or bacteria enter the body, they react with histamine--a neurotransmitter that triggers an inflammation response. By binding to histamines, antihistamines like diphenhydramine (commonly found in Benadryl) prevent histamines from signaling an inflammatory response. Without the inflammatory response, a person will see a decrease in runny nose, itchy, watery eyes and other symptoms of a cold or allergies.

Common Antihistamines

• Diphenhydramine is commonly found in Benadryl and many other generic over-the-counter medicines for cold and allergy. Loratadine is found in Claritin.

History

• Antihistamines have been around since the 1940s.

Side Effects

• The most common side effect of antihistamines is drowsiness, and indeed many antihistamines are used as sedatives.

Recreational Use

• The sedative power of antihistamines makes them candidates for abuse. A heavy overdose of antihistamines can cause heart attack.