Diphenhydramine injection is an antihistamine used to treat life-threatening allergic reactions (anaphylaxis) along with epinephrine and other treatments. It is also used to relieve symptoms of household allergies, hay fever and the common cold when medication cannot be given by mouth. Common allergy symptoms relieved by antihistamines include rash, itching, watery eyes, itchy eyes/nose/throat, cough, runny nose and sneezing. It is also used to treat nausea, vomiting and dizziness caused by motion sickness when medication cannot be given by mouth. Diphenhydramine works by blocking a certain natural substance (histamine) that your body makes during an allergic reaction. Its drying effects on such symptoms as watery eyes and runny nose are caused by blocking another natural substance made by your body (acetylcholine). Diphenhydramine should not be used in newborns or premature infants because of an increased risk of side effects. It should not be used for common cold symptoms in children less than 6 years of age due to the risk of serious side effects, such as slow/shallow breathing. Cough-and-cold products have not been shown to be safe or effective in children younger than 6.
Drowsiness, dizziness, headache, irritability, stomach upset, vision changes (e.g., blurred vision), decreased coordination, constipation, or dry mouth/nose/throat may occur. These effects may decrease as your body adjusts to the medication. If they persist or become bothersome, inform your doctor. To relieve dry mouth, suck on (sugarless) hard candy or ice chips, chew (sugarless) gum, drink water or use a saliva substitute. Diphenhydramine can dry up and thicken the mucus in your lungs, making it more difficult to breathe and clear your lungs. To help prevent this effect, be sure to drink plenty of fluids unless otherwise directed by your physician. Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor right away if you have any serious side effects, including: mental/mood changes (such as restlessness, confusion), pounding/irregular heartbeat, ringing in the ears, seizure, difficulty urinating. A very serious allergic reaction to this drug is unlikely, but get medical help right away if it occurs. Symptoms of a serious allergic reaction may include: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.
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