antihistamine antihistamine antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provides relief from nasal congestion, sneezing, or hives caused by pollen, dust mites, or animal allergy with few side effects. antihistamines are usually for short-term treatment. chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and lower respiratory tract infection. consultation of a medical professional is recommended for those who intend to take antihistamines for longer-term use. antihistaminedrug classhistamine structureclass identifierspronunciation/ˌæntiˈhɪstəmiːn/ atc coder06mechanism of action • receptor antagonist • inverse agonistbiological targethistamine receptors • hrh1 • hrh2 • hrh3 • hrh4