Benadryl (diphenhydramine) is a brand-name over-the-counter drug that’s used for allergies and itchy skin. Learn about side effects, price, and more. Learn about Benadryl: What is it used for, what you need to know before taking, important warnings and safety info, how to take, side effects and more. Benadryl (diphenhydramine) is an antihistamine used to treat allergies, hives, insomnia, motion sickness, and mild cases of Parkinsonism. Benadryl is available in generic form and over-the-counter (OTC). Find patient medical information for Diphenhydramine (Benadryl, Unisom, and others) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings What is BENADRYL® and what is in the products? BENADRYL ® is an antihistamine that works to relieve your allergies when you need it the most. Our products contain diphenhydramine HCl, which helps treat allergy symptoms at the source. Benadryl is an antihistamine and is used to treat sneezing, runny nose, itching and other allergies. Learn about side effects, interactions and indications. Diphenhydramine, also known by the brand name Benadryl, is an over-the-counter antihistamine used to relieve allergy or common cold symptoms in adults and children. 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. 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 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.