What are antihistamines? Give two examples? Explain how do they act on the human body?

Explanation

The hypersensitivity of some persons towards certain drugs, dust, pollengrains, cat fur, or food etc. is called allergy. Allergy is caused by release of a substance called histamine in the body. Antihistamines are drugs which either reduce or inhibit the action of histamine in the body thereby preventing allergy.
Mode of action
Histamines interact with the building sites of receptor in the body to produce allergy. Antihistamines compete with histamines for these binding sites of receptor and thus preventing histamine producing allergy. Thus antihistamines are drugs which interfere with the natural action of histamine by competing for histamine binding sites of receptor.