Class Name(s):

• 4:04 First Generation Antihistamines

Pronunciation:

• (dye fen hye' dra meen)

Brand Name(s):

• Benadryl¶; also available generically

WHY is this medicine prescribed?

Diphenhydramine injection is used to treat allergic reactions. It is used also to treat motion sickness. Diphenhydramine injection is also used to control abnormal movements in people who have Parkinsonian syndrome (a disorder of the nervous system that causes difficulties with movement, muscle control, and balance). Diphenhydramine injection is in a class of medications called antihistamines. It works by blocking the action of histamine, a substance in the body that causes allergic symptoms.

HOW should this medicine be used?

Diphenhydramine injection comes as a solution (liquid) to be injected intramuscularly (into a muscle) or intravenously (into a vein). Your dosing schedule will depend on your condition and on how you respond to treatment.

You may receive diphenhydramine injection in a hospital, office, or you may administer the medication at home. If you will be using diphenhydramine injection at home, your healthcare provider will show you how to use the medication. Be sure that you understand these directions, and ask your healthcare provider if you have any questions.

Are there OTHER USES for this medication?

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What SPECIAL PRECAUTIONS should I follow?

Before using diphenhydramine injection,

• tell your doctor or pharmacist if you are allergic to this drug, any part of this drug, or any other drugs, foods or substances. Tell your doctor or pharmacist about the allergy and what symptoms you had.
• tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take while receiving diphenhydramine injection. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• tell your doctor if you have or have ever had asthma or other types of lung disease; glaucoma (a condition in which increased pressure in the eye can lead to gradual loss of vision); ulcers; prostatic hypertrophy (enlargement of the prostate gland) or difficulty urinating (due to an enlarged prostate gland); heart disease; high blood pressure; or hyperthyroidism (a condition where the thyroid gland produces too much thyroid hormone).
• tell your doctor if you are pregnant or plan to become pregnant. If you become pregnant while using diphenhydramine injection, call your doctor.
• tell your doctor if you are breastfeeding. Your doctor will probably tell you not to receive diphenhydramine injection if you are breastfeeding because of the risk of harm to infants.
• you should know that diphenhydramine injection may make you drowsy. Do not drive a car or operate machinery until you know how this medication affects you.
• ask your doctor about the safe use of alcoholic beverages while you are using diphenhydramine injection. Alcohol can make the side effects from diphenhydramine injection worse.

What SPECIAL DIETARY instructions should I follow?

Unless your doctor tells you otherwise, continue your normal diet.

What SIDE EFFECTS can this medicine cause?

Diphenhydramine injection may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• dizziness, tiredness, problems with coordination
• restlessness, excitement (especially in children)
• stomach discomfort
• difficulty urinating
• change in urinary frequency
• dry mouth, nose, or throat; thickening of mucous

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately or get emergency medical treatment:

• rash, hives, wheezing
• seizures

Diphenhydramine injection may cause other side effects. Call your doctor if you have any unusual problems while using this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

What should I do in case of OVERDOSE?

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at http://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

Symptoms of overdose may include the following:

• dry mouth
• dilated pupils (black circles in the centers of the eyes)
• flushing

What should I know about STORAGE and DISPOSAL of this medication?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from light, excess heat and moisture (not in the bathroom).

Dispose of unneeded medications in a way so that pets, children, and other people cannot take them. Do not flush this medication down the toilet. Use a medicine take-back program. Talk to your pharmacist about take-back programs in your community. Visit the FDA's Safe Disposal of Medicines website http://goo.gl/c4Rm4p for more information.

Keep all medication out of sight and reach of children as many containers are not child-resistant. Always lock safety caps. Place the medication in a safe location - one that is up and away and out of their sight and reach. http://www.upandaway.org

What OTHER INFORMATION should I know?

Ask your pharmacist any questions you have about diphenhydramine injection.

Keep a written list of all of the prescription and nonprescription (over-the-counter) medicines, vitamins, minerals, and dietary supplements you are taking. Bring this list with you each time you visit a doctor or if you are admitted to the hospital. You should carry the list with you in case of emergencies.

^¶ This branded product is no longer on the market. Generic alternatives may be available.

This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists, Inc. represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists, Inc. makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

AHFS^® Patient Medication Information™ Copyright, 2025. The American Society of Health-System Pharmacists^®, 4500 East-West Highway, Suite 900, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: August 15, 2025.