What is Benadryl (diphenhydramine)? Benadryl is a brand) name for diphenhydramine hydrochloride, a sedating antihistamine used to treat allergies, sleep problems, and motion sickness. Benadryl is a brand of various antihistamine medications used to treat allergies, whose content varies in different countries, but which includes some combination of diphenhydramine, acrivastine, or cetirizine. Do you need help relieving allergies or a pesky itch? Check out the many allergy and itch relief products BENADRYL® offers which may help provide relief. Find BENADRYL® dosage information for adults, children, and toddlers and learn how much you and your family should take with our allergy medicine product-dosing guide. Diphenhydramine, or Diphenylhydramine, sold under the brand name Benadryl among others, is an antihistamine and sedative. Although generally considered sedating, diphenhydramine can cause paradoxical central nervous system stimulation in some individuals, particularly at higher doses. Benadryl® (diphenhydramine) is a liquid medication that treats the symptoms of allergies and allergic reactions. It may also prevent and treat motion sickness or the symptoms of Parkinson’s disease. Benadryl is an antihistamine that reduces the effects of natural chemical histamine in the body. Histamine can produce symptoms of sneezing, itching, watery eyes, and runny nose. Benadryl is used to treat sneezing, runny nose, watery eyes, hives, skin rash, itching, and other cold or allergy symptoms.