BENADRYL ULTRA, TAB 25MG (24/CT) Diphenhydramine is an antihistamine used to relieve symptoms of allergy, hay fever, and the common cold These symptoms include rash, itching, watery eyes, itchy eyes/nose/throat, cough, runny nose, and sneezing It is also used to prevent and treat nausea, vomiting and dizziness caused by motion sickness As a sleep aid, diphenhydramine should be takenapproximately 30 minutes before bedtime