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. What is Benadryl used for? Benadryl is used to ease allergy signs. It is used to help motion sickness. Benadryl is also used to treat signs like Parkinson's disease caused by other health problems. Benadryl starts working within 30 minutes after taking it orally, with peak effects reached in 1-2 hours. The antihistamine effects last 4-6 hours for most people. Injectable Benadryl works even faster than oral tablets, providing quicker relief for severe allergic reactions. 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. 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. 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. Benadryl (diphenhydramine) is primarily used to treat allergic reactions, but it also has several other legitimate uses, including as a short-term sleep aid, a motion sickness remedy, and a treatment for certain movement disorders. 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 patient medical information for Diphenhydramine (Benadryl, Unisom, and others) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings.