Histamine antagonist/Definition

A member of a class of drug that binds to cell surface receptors for histamine1, histamine2, and histamine3 receptors, preventing them from activating. The receptor types have a variety of functions; histamine1 activities include allergic reactions and nausea, histamine2 reduce gastric acid secretion and relax smooth muscle, and histamine3, still in research, have central nervous system effects. "Antihistamines" are most often histamine1 blockers.