Antihistamine

Antihistamines or histamine antagonists are a group of pharmaceuticals that prevent histamines from binding to their receptors in cells. Most antihistamines also produce the opposite effect from histamines, actually reducing swelling and inflammation. They're useful in preventing and counteracting the most common symptoms of an allergy, such as runny nose, nasal congestion, sneezing, excess production of tears, and skin irritation. In addition, they can be used to prevent excess stomach acid production.
Most of the older antihistamines have a sedative effect, and must be avoided where alertness is important. They're still widely used for nighttime use. Some modern antihistamines have the opposite effect - they act as stimulants and are generally used for daytime use as they can cause insomnia.
Histamine antagonist at Wikipedia
Category:Pharmaceuticals