diphenhydramine

Diphenhydramine is an antihistamine that reduces the effects of natural chemical histamine in the body. Histamine can produce symptoms of sneezing, itching, watery eyes, and runny nose.

Diphenhydramine is used to treat sneezing, runny nose, watery eyes, hives, skin rash, itching, and other cold or allergy symptoms.

Diphenhydramine is also used to treat motion sickness, to induce sleep, and to treat certain symptoms of Parkinson"s disease.

Diphenhydramine may also be used for purposes not listed in this medication guide.

Important information

When taking diphenhydramine, use caution driving, operating machinery, or performing other hazardous activities. Diphenhydramine may cause dizziness or drowsiness. If you experience dizziness or drowsiness, avoid these activities.

Use alcohol cautiously. Alcohol may increase drowsiness and dizziness while taking diphenhydramine.

Do not give this medication to a child younger than 2 years old. Always ask a doctor before giving a cough or cold medicine to a child. Death can occur from the misuse of cough and cold medicines in very young children.

Before taking this medicine

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

Ask a doctor or pharmacist if it is safe for you to take diphenhydramine if you have other medical conditions, especially:

• blockage in your digestive tract (stomach or intestines);

• bladder obstruction or other urination problems;

• a colostomy or ileostomy;

• liver or kidney disease;

• asthma, chronic obstructive pulmonary disease (COPD), or other breathing disorder;

• cough with mucus, or cough caused by smoking, emphysema, or chronic bronchitis;

• heart disease, low blood pressure;

• glaucoma;

• a thyroid disorder; or

• if you take potassium (Cytra, Epiklor, K-Lyte, K-Phos, Kaon, Klor-Con, Polycitra, Urocit-K).

FDA pregnancy category B. Diphenhydramine is not expected to harm an unborn baby. Do not use this medicine without a doctor"s advice if you are pregnant.

See also: Pregnancy and breastfeeding warnings (in more detail)

Diphenhydramine can pass into breast milk and may harm a nursing baby. You should not breast-feed while using this medicine.

Older adults may be more likely to have side effects from this medicine.

How should I take diphenhydramine?

Use 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. Cold or allergy medicine is usually taken only for a short time until your symptoms clear up.

Do not give diphenhydramine to a child younger than 2 years old. Always ask a doctor before giving a cough or cold medicine to a child. Death can occur from the misuse of cough and cold medicines in very young children.

Measure liquid medicine with a special dose-measuring spoon or medicine cup. If you do not have a dose-measuring device, ask your pharmacist for one.

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.

Call your doctor if your symptoms do not improve after 7 days of treatment, or if you have a fever with a headache, cough, or skin rash.

This medication 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 happens if I miss a dose?

Since diphenhydramine is used when needed, you may not be on a dosing schedule. If you are on a schedule, use the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not use extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid?

This medication may cause blurred vision and may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert and able to see clearly.

Drinking alcohol can increase certain side effects of diphenhydramine.

Ask a doctor or pharmacist before using any other cold, cough, allergy, or sleep medicine. Antihistamines are contained in many combination medicines. Taking certain products together can cause you to get too much of this type of medicine. Check the label to see if a medicine contains an antihistamine.

Diphenhydramine side effects

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

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

• pounding heartbeats or fluttering in your chest;

• painful or difficult urination;

• little or no urinating;

• confusion, feeling like you might pass out; or

• tightness in your neck or jaw, uncontrollable movements of your tongue.

Common diphenhydramine side effects may include:

• dizziness, drowsiness, loss of coordination;

• dry mouth, nose, or throat;

• constipation, upset stomach;

• dry eyes, blurred vision; 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.

See also: Side effects (in more detail)

Diphenhydramine dosing information

Usual Adult Dose of Diphenhydramine for Extrapyramidal Reaction:

Parenteral: 10 to 50 mg IV or IM as needed. May increase dose to 100 mg if required. Maximum daily dose 400 mg.

Oral: 25 to 50 mg orally every 6 to 8 hours.

Usual Adult Dose for Insomnia:

25 to 50 mg orally at bedtime.

Usual Adult Dose of Diphenhydramine for Motion Sickness:

Parenteral: 10 to 50 mg IV or IM as needed. May increase dose to 100 mg if required. Maximum daily dose 400 mg.

Oral: 25 to 50 mg orally every 6 to 8 hours. Administer first dose 30 minutes before exposure to motion and repeat before meals and upon retiring for the duration of the journey.

Usual Adult Dose for Cough:

25 mg orally every 4 hours as needed, not to exceed 150 mg per day.

Usual Adult Dose of Diphenhydramine for Cold Symptoms:

25 to 50 mg orally every 4 to 6 hours as needed, not to exceed 300 mg/24 hours.

Usual Adult Dose for Pruritus:

25 to 50 mg orally every 4 to 6 hours as needed, not to exceed 300 mg/24 hours.

Usual Adult Dose of Diphenhydramine for Urticaria:

25 to 50 mg orally every 4 to 6 hours as needed, not to exceed 300 mg/24 hours.

Usual Pediatric Dose for Allergic Rhinitis:

Greater than or equal to 2 to less than 6 years: 6.25 mg orally every 4 to 6 hours, not to exceed 37.5 mg/24 hours.

Greater than or equal to 6 to less than 12 years: 12.5 to 25 mg orally every 4 to 6 hours, not to exceed 150 mg/24 hours.

Greater than or equal to 12 years: 25 to 50 mg orally every 4 to 6 hours, not to exceed 300 mg/24 hours.

Usual Pediatric Dose for Cold Symptoms:

Greater than or equal to 2 to less than 6 years: 6.25 mg orally every 4 to 6 hours, not to exceed 37.5 mg/24 hours.

Greater than or equal to 6 to less than 12 years: 12.5 to 25 mg orally every 4 to 6 hours, not to exceed 150 mg/24 hours.

Greater than or equal to 12 years: 25 to 50 mg orally every 4 to 6 hours, not to exceed 300 mg/24 hours.

Usual Pediatric Dose for Motion Sickness:

Greater than or equal to 2 to less than 6 years: 6.25 mg orally every 4 to 6 hours, not to exceed 37.5 mg/24 hours.

Greater than or equal to 6 to less than 12 years: 12.5 to 25 mg orally every 4 to 6 hours, not to exceed 150 mg/24 hours.

Greater than or equal to 12 years: 25 to 50 mg orally every 4 to 6 hours, not to exceed 300 mg/24 hours.

Usual Pediatric Dose for Insomnia:

Greater than or equal to 12 years: 25 to 50 mg orally at bedtime.

Usual Pediatric Dose for Cough:

Greater than or equal to 2 to less than 6 years: 6.25 mg orally every 4 hours, not to exceed 37.5 mg/24 hours.

Greater than or equal to 6 to less than 12 years: 12.5 mg orally every 4 hours, not to exceed 75 mg/24 hours.

Greater than or equal to 12 years: 25 mg orally every 4 hours, not to exceed 150 mg/24 hours.

Usual Pediatric Dose for Extrapyramidal Reaction:

In dystonic reactions: 1 to 2 mg/kg (max: 50 mg) IV or IM [Pediatric Advanced Life Support]

Usual Pediatric Dose for Allergic Reaction:

1 to 12 years: 5 mg/kg/day or 150 mg/m2/day administered orally, IM or IV, in equally divided doses every 6 to 8 hours, not to exceed 300 mg/24 hours.

In acute hypersensitivity reactions: 1 to 2 mg/kg IV or IM (max: 50 mg) [Advanced Pediatric Life Support]

What other drugs will affect diphenhydramine?

Ask a doctor or pharmacist before using this medicine if you are also using any other drugs, including prescription and over-the-counter medicines, vitamins, and herbal products. Some medicines can cause unwanted or dangerous effects when used together. Not all possible interactions are listed in this medication guide.

Taking this medicine with other drugs that make you sleepy or slow your breathing can worsen these effects. Ask your doctor before taking diphenhydramine with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures.