Diphenhydramine is an over-the-counter (OTC) medicine used to treat symptoms of allergies, hay fever, or the common cold. It may help relieve:

Watery, itchy, red, or irritated eyes
Runny nose
Sneezing
Hives
Itching

The medicine is also taken to help treat or prevent insomnia or motion sickness. Additionally, diphenhydramine is used to control abnormal movements in people with early-stage Parkinson’s disease.

Diphenhydramine is in a class of drugs called antihistamines, which work by blocking the action of a natural substance called histamine.

It’s sold under the brand name Benadryl.

warnings

What is the most important information I should know about Benadryl (Diphenhydramine)?

You should not use diphenhydramine if you are allergic to it.

Ask a doctor or pharmacist if this medicine is safe to use if you have ever had:

an enlarged prostate or urination problems;
asthma, chronic obstructive pulmonary disease (COPD), or other breathing disorder;
glaucoma; or
a thyroid disorder.

Ask a doctor before using this medicine if you are pregnant or breastfeeding. Diphenhydramine may slow breast milk production.

Side Effects

What are the side effects of Benadryl (Diphenhydramine)?

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using diphenhydramine and call your doctor at once if you have:

severe drowsiness; or
painful or difficult urination.

Side effects such as dry mouth, constipation, and confusion may be more likely in older adults.

Common side effects may include:

drowsiness;
dry eyes, blurred vision;
dry mouth, nose, or throat;
decreased urination;
constipation;
feeling restless or excited (especially in children); or
day-time drowsiness or "hangover" feeling after night-time use.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Interactions

What drugs and food should I avoid while taking Benadryl (Diphenhydramine)?

Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.

Drinking alcohol can increase certain side effects of diphenhydramine.

Ask a doctor or pharmacist before using any other medicine that may contain diphenhydramine. This includes medicines for sleep, cold/allergy symptoms, or anti-itch medicine used on the skin. Using too much diphenhydramine may lead to a fatal overdose.

Dosage Guidelines & Tips

How to take Benadryl (Diphenhydramine)?

Use Benadryl (Diphenhydramine) exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

Use exactly as directed on the label, or as prescribed by your doctor. Diphenhydramine is only for short-term use until your symptoms clear up.

Taking too much diphenhydramine can lead to serious heart problems, seizures, coma, or death.

Always follow directions on the medicine label about giving diphenhydramine to a child. Do not use the medicine only to make a child sleepy. Death can occur from the misuse of antihistamines in very young children.

For motion sickness, take diphenhydramine 30 minutes before you will be in a situation that causes you motion sickness (such as a long car ride, airplane or boat travel, amusement park rides, etc). Continue taking diphenhydramine with meals and at bedtime for the rest of the time you will be in a motion-sickness situation.

As a sleep aid, take diphenhydramine within 30 minutes before bedtime.

You must chew the chewable tablet before you swallow it.

Measure liquid medicine carefully. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

Remove an orally disintegrating tablet from the package only when you are ready to take the medicine. Place the tablet in your mouth and allow it to dissolve, without chewing. Swallow several times as the tablet dissolves.

Call your doctor if the condition you are treating with diphenhydramine does not improve, or if you have a fever with a headache, cough, or skin rash.

Do not use diphenhydramine for longer than 2 weeks to treat sleep problems, or longer than 7 days to treat cold or allergy symptoms.

This medicine can affect the results of allergy skin tests. Tell any doctor who treats you that you are using diphenhydramine.

Store at room temperature away from moisture and heat.

What should I do if I missed a dose of Benadryl (Diphenhydramine)?

Since diphenhydramine is used when needed, you may not be on a dosing schedule. Skip any missed dose if it's almost time for your next dose. Do not use two doses at one time.

Overdose Signs

What happens if I overdose on Benadryl (Diphenhydramine)?

Overdose symptoms may include vomiting, confusion, severe drowsiness, ringing in your ears, no urination, very dry eyes and mouth, dilated pupils, fast heartbeats, tremor, agitation, hallucinations, or seizure.

If you think you or someone else may have overdosed on: Benadryl (Diphenhydramine), call your doctor or the Poison Control center

(800) 222-1222

If someone collapses or isn't breathing after taking Benadryl (Diphenhydramine), call 911

911