Diphenhydramine is a common ingredient in sleeping aids; it is also used to treat allergies. While effective, the risk of serious diphenhydramine side effects—including confusion, dizziness, urinary retention, and liver or kidney issues—is increased in people age 65 and older. 1 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 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. It comes as pills and a liquid and is typically taken by mouth every 4 to 6 hours as needed. Because it can make you drowsy, some people also use it as a sleep aid at bedtime. Common side effects include sleepiness, dizziness, and. Diphenhydramine is an antihistamine used to treat sneezing, runny nose, itching, hives and other symptoms of allergies and the common cold. Includes diphenhydramine side effects, interactions and indications. Diphenhydramine is also available in combination with other medications. This monograph only includes information about the use of diphenhydramine alone. If you are taking the combination product, read the information on the package label or ask your doctor or pharmacist for more information. Diphenhydramine, 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. Diphenhydramine is an antihistamine medication that treats the symptoms of allergies, allergic reactions, motion sickness and symptoms of Parkinson’s disease. NHS medicines information on diphenhydramine – what it's used for, side effects, dosage and who can take or use it. Diphenhydramine is a prescription medication used to treat the symptoms of an allergic reaction, insomnia, cough, motion sickness, and parkinsonism. Learn about side effects, dosages, drug interactions, warnings, and more. In a new review, experts call for the removal of diphenhydramine from over-the-counter and prescription markets in the United States, saying it’s outdated, dangerous and eclipsed by safer.