Diphenhydramine HCl, commonly known as Benadryl, is an antihistamine used to treat sneezing, runny nose and red, irritated, itchy or watery eyes caused by hay fever, allergies or the common cold. It is sometimes used to relieve cough, prevent or treat motion sickness and treat insomnia, states MedlinePlus. Patients who experience movement problems as a result of medications or early-stage parkinsonian syndrome may take diphenhydramine to control abnormal movements.
Diphenhydramine can cause side effects, including drowsiness, dizziness, nausea, vomiting, loss of appetite, constipation, headache, muscle weakness, nervousness, increased chest congestion and dry mouth, nose and throat. MedlinePlus states that excitement is a side effect that is often experienced by children. It is best to report these side effects to a doctor if they are severe or unrelieved. Prompt medical attention is recommended for serious side effects, which include vision problems and difficult or painful urination.
MedlinePlus advises patients who have lung problems, glaucoma, ulcers, an enlarged prostate, heart disease, high blood pressure, seizures or an overactive thyroid to contact their doctor before taking diphenhydramine. Administering diphenhydramine to children under 4 years old is not recommended because of the potential for serious side effects. Caution is advised when giving diphenhydramine to children between the ages of 4 and 11.