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Adult Allergy Oral

Generic Name: DIPHENHYDRAMINE - ORAL
Pronounced: (dye-fen-HI-druh-meen)

Adult Allergy Oral Side Effects

Drowsiness, dizziness, headache, constipation, stomach upset, vision changes (e.g., blurred vision), irritability, decreased coordination, or dry mouth/nose/throat may occur. These effects may decrease as your body adjusts to the medication. If any of these effects persist or worsen, 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 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.

If your doctor has directed you to use this medication, remember that 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 immediately if any of these rare but serious side effects occur:

  • pounding/irregular heartbeat
  • ringing in the ears
  • seizure
  • difficulty urinating


A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention 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.

Call your doctor for medical advice about side effects. In the US, you may report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088.

In Canada, you may report side effects to Health Canada at 1-866-234-2345.

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