Final answer:
Antihistamines are drugs that treat allergies by reducing the effects of histamines. They bind to specific receptors in the body and are classified into H₁-antihistamines and H₂-antihistamines.
Step-by-step explanation:
Antihistamines are drugs that treat hay fever and other allergies by reducing or eliminating the effects of histamines, which produce allergy symptoms. They work by binding to specific histamine receptors in the body. The two largest classes of antihistamines are H₁-antihistamines and H₂-antihistamines. H₁-antihistamines are used to treat allergic reactions in the nose, while H₂-antihistamines are used to treat gastric acid conditions.