Common side effects of diphenhydramine citrate include drowsiness, dizziness, stomach upset, blurred vision, and dryness in the mouth, nose or throat. More serious side effects include mental changes, such as restlessness or confusion; difficulty urinating; and a fast or irregular heartbeat. A person experiencing extremely serious side effects, such as seizure or allergic reaction, should seek medical care immediately, warns WebMD. Children and the elderly may be more sensitive to the side effects of this medicine.
Because diphenhydramine citrate can cause drowsiness or blurred vision, people should not drive or operate machinery after taking this medicine unless they are certain they can do so safely, urges WebMD. People should also avoid drinking alcohol while on this medicine. Topical antihistamines, such as itch cream, may interact with this medicine, as can other medicines that cause drowsiness. A person should confirm with his doctor or pharmacist that it is safe to take this medicine with his other current medicines. Diphenhydramine can interfere with lab tests and cause false positives, so people taking this medicine should inform laboratory staff prior to testing.
Diphenhydramine citrate is an antihistamine that relieves symptoms of allergies or colds, such as runny nose, sneezing and coughing, says WebMD. It also helps people fall asleep and is useful for preventing and treating motion sickness.