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Brand names:

Benadryl®, Nytol®, PediaCare Children’s Allergy®, Unisom®

Other names:

Diphenhydramine hydrochloride

Often used for:

Symptoms associated with allergies or hay fever, colds, and allergic reactions

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About Diphenhydramine

Diphenhydramine is an antihistamine. This type of medicine acts to block the activity of the histamine, a substance that causes allergy symptoms.

Diphenhydramine can be used to treat a variety of symptoms including:

  • Allergy and cold symptoms such as irritated and itchy eyes, sneezing, and runny nose
  • Coughing
  • Motion sickness and nausea
  • Sleep problems
  • Movement problems
  • Allergic reactions such as rash, itching, swelling

This medicine is often used in combination with other medicines such as pain relievers, fever reducers, and decongestants.

This medicine is available in prescription and over-the-counter (OTC) forms.

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May be given as a liquid injected into a muscle or vein

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May be taken as a tablet, capsule, or dissolvable tablet or strip by mouth

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May be taken as a liquid by mouth

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Possible Side Effects

  • Nausea and vomiting
  • Drowsiness or dizziness
  • Constipation
  • Headache
  • Feeling tired
  • Feeling nervous or excitable
  • Increased congestion of nose or chest

Not all patients who take diphenhydramine will experience these side effects. Common side effects are in bold, but there may be others. Please report all suspected side effects to your doctor or pharmacist.

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Tips for Families

Be sure to discuss these and other recommendations with your doctor or pharmacist.

  • Diphenhydramine is often used on an as-needed basis.
  • Families should talk to a doctor or pharmacist before using diphenhydramine, even when using over-the-counter medicine in children under 6 years old. Follow dosing instructions, and use as directed.
  • Be careful when using more than one cold or allergy medicine at the same time. These products may have the same ingredients, and using them together could cause an overdose. Read the label carefully, and discuss any questions with a doctor or pharmacist.

Diphenhydramine at home:

  • Do not take more often or in greater amounts than recommended.
  • Take with food if stomach upset occurs.
  • Capsules should be swallowed whole. Do not crush or chew before swallowing.
  • Chewable tablets should be chewed completely before swallowing.
  • Oral-disintegrating tablets or dissolvable strips should be allowed to melt on the tongue and then swallowed with a sip of liquid.
  • For liquid diphenhydramine, use the measuring device that comes with the medicine.
  • Store medicine at room temperature.
  • If taking diphenhydramine on a regular basis, give a missed dose as soon as possible. If it is near the time for the next dose, skip the dose. Do not give 2 doses at the same time. 
  • Do not use the medicine past the expiration date.
  • Follow instructions for safe storage and disposal.