The Function of Antihistamines

Antihistamines bring comfort and relief to many allergy sufferers around the world. There are two types of these drugs: prescription and over-the-counter. Both types, if taken properly, provide instant relief to allergic reactions due to allergy. The common reactions from allergies include sneezing, itching of the affected part, nasal congestion, headache, and others. The normal cause of such reactions is due to exposure to allergens such as pollen, dust, or insect venom.

When your body reacts to these allergens, your blood will produce antibodies such as histamine to try to defeat the "invaders". The severity of the allergic reaction is directly proportional to the amount of histamine produced in the blood. Histamines dilate tiny blood vessels and capillaries, but cause the smooth muscles to contract. If this happens, histamine should be lowered dramatically or prevented to rise further. The main function of antihistamine is to prevent the production of more histamine. This drug cannot reverse the effects of histamines though.

Normally, antihistamines are taken orally since they can be absorbed by the intestines well. Some forms of this drug can also be taken intravenously. They are normally taken 2 to 4 times a day since the liver rapidly metabolizes them.