Antihistamines

Antihistamines: Blocking Histamine's Receptor, Not Its Production

Histamine is a chemically potent signalling molecule with several physiological effects: it is a powerful vasodilator (it widens blood vessels), it contracts smooth muscle in the bronchi (airways) and gut, it relaxes muscle in the walls of fine blood vessels, and it is responsible for the nasal congestion typical of the common cold and of allergic reactions to substances such as pollen.

Mechanism of antihistamine drugs. Synthetic antihistamine drugs act by competing directly with histamine for its receptor binding sites on target cells - by occupying the receptor first, the drug prevents histamine from binding there and triggering its effects, without altering how much histamine the body actually produces. …