Subscribe

Medically Reviewed by Andrea Wessell, PharmD, BCPS on Nov 20, 2024 | Written by Sandra Chabot, PharmD

Overview: Diphenhydramine is an antihistamine that is used to help treat certain allergy or common cold symptoms, allergic reactions, trouble sleeping, motion sickness, or certain movement problems. Common side effects may include drowsiness, dizziness, and stomach upset. It may cause excitability in children. Do not drive or do other activities that require alertness, coordination, or clear vision until you know how diphenhydramine affects you. Call your health care provider right away if you are having trouble peeing or cannot empty your bladder while taking diphenhydramine.

Uses

What is diphenhydramine used for?

Diphenhydramine is commonly used for the following conditions. 

• Allergy or common cold symptoms, such as a runny nose, sneezing, itchy or watery eyes, an itchy nose or throat, or cough
• Trouble falling asleep (insomnia)
• Motion sickness
• Certain types of allergic reactions, including reactions to blood or plasma transfusions or for anaphylaxis
• Involuntary movement problems called parkinsonism

These uses may vary depending on the specific diphenhydramine product used. Diphenhydramine may also be used for other conditions as determined by your health care provider.

How does diphenhydramine work (mechanism of action)?

Diphenhydramine is an antihistamine. It works by blocking the effect of a substance in your body called histamine.

How is diphenhydramine supplied (dosage forms)?

Brands and other names

• Banophen
• Benadryl
• Dibenil
• Diphen
• Hydramine
• Nervine
• Nytol
• QlearQuil
• Simply Sleep
• Sominex
• Unisom
• ZzzQuil

Example dosage forms and strengths

• 12.5 mg/5 mL, 50 mg/30 mL oral elixir/liquid/solution/syrup
• 12.5 mg, 25 mg chewable tablets/soft chews
• 25 mg, 50 mg oral tablets
• 25 mg, 50 mg oral capsules

Diphenhydramine is also available in injectable forms.

Diphenhydramine is also available in a form that is applied to the skin. See Diphenhydramine topical for more information. 

How should I store diphenhydramine?

Oral Products. Diphenhydramine products that you take by mouth should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). They can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting them. Store in a cool, dry place. Protect from light. 

Injectable Liquid. Diphenhydramine injection is usually given by a health care provider in a hospital or clinic. You will not store it at home.

Side Effects

What are the most common side effects of diphenhydramine?

The most common side effects of diphenhydramine are listed below. Tell your health care provider if you have any of these side effects that bother you.

• Drowsiness or tiredness
• Excitability (especially in children)
• Dizziness or feeling off-balance
• Stomach upset
• Increase in thickness of mucus in the lungs

There may be other side effects of diphenhydramine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of diphenhydramine?

While less common, the most serious side effects of diphenhydramine are described below, along with what to do if they happen.

Severe Allergic Reactions. Diphenhydramine may cause allergic reactions, which can be serious. Stop using diphenhydramine and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching, skin rash, or pale red bumps on the skin called hives
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain

Seizures. Some people who have taken diphenhydramine have reported having convulsions, also known as seizures. This may be more common in children. There are many different types of seizures and some of them are not easy to recognize. Stop taking diphenhydramine and call your health care provider if you have any of the following signs that a seizure is happening or could happen.

• Muscle twitching, jerking, spasms, tremors, or other uncontrolled movements
• Stiffening of your arms and legs
• Feeling anxious, nervous, confused, or a sense of dread
• Feeling dizzy or lightheaded
• Falling or losing consciousness

Inability to Empty Bladder (Urinary Retention). Diphenhydramine might make it harder to empty your bladder, especially if you already have a blockage. Stop taking diphenhydramine and call your health care provider right away if you are having trouble peeing or cannot empty your bladder.

Warnings & Precautions

Who should not use diphenhydramine?

Allergies to Ingredients. People who are allergic to any of the following should not use diphenhydramine.

• Benadryl
• Diphenhydramine
• Any other medicine known as a first-generation antihistamine 
• Any of the ingredients in the specific product being used

Your pharmacist can tell you all of the ingredients in the specific diphenhydramine products they stock.

Infants. Diphenhydramine injection should not be used in newborn or premature babies. This medicine can cause serious side effects in these infants. 

Breastfeeding. Do not use diphenhydramine if you are breastfeeding. You must either stop breastfeeding or stop diphenhydramine. See the Breastfeeding section for more details.

What should I know about diphenhydramine before using it?

If diphenhydramine was prescribed to you by a health care provider, use it as prescribed. If you are using over-the-counter (OTC) diphenhydramine, follow the instructions that come with the product.

Do not share diphenhydramine that was prescribed for you by a health care provider with other people, even if they have the same condition as you. It may harm them.

Keep diphenhydramine out of the reach of children.

There are several forms of diphenhydramine available. Read and follow the instructions for the product you have and make sure you understand how to use it properly. If you have any questions, talk to your pharmacist or other health care provider.

If you are taking diphenhydramine chewable tablets, they should be chewed or crushed completely before swallowing them. Do not swallow them whole.

If you are taking diphenhydramine liquid, use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist what measuring device to use.

Do not use diphenhydramine to make a child sleepy. Talk with your health care provider if you have questions. 

Diphenhydramine can affect your alertness or coordination and may cause your vision to be blurry. Do not drive or do other activities that require alertness, coordination, or good vision until you know how diphenhydramine affects you.

Diphenhydramine can make your skin more sensitive to light from the sun, sunlamps, and tanning beds. This is called photosensitivity. Exposure to this light can cause severe sunburns, blisters, and swelling. If you need to be in sunlight, wear sunscreen, a hat, and clothing that covers your skin.

People who are 60 and older or those younger than 18 can be at greater risk of some side effects from diphenhydramine. Talk to your health care provider about your risks if you are in this age group.

If you have a cough that lasts for longer than one week or comes back after going away, stop using diphenhydramine and contact your health care provider. Also tell your health care provider if you have a cough with a rash, fever, or headache that will not go away. These could be symptoms of a serious condition. 

If you are taking diphenhydramine for sleep, tell your health care provider if you have trouble sleeping for more than two weeks. Your health care provider may need to see if a medical condition is causing your sleep problems. 

What should I tell my health care provider before using diphenhydramine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if diphenhydramine is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following. 

• Breathing problems, such as asthma or chronic obstructive pulmonary disease (COPD)
• A cough with a lot of phlegm (mucus) or a long-lasting cough
• Increased pressure in your eyes or glaucoma
• Stomach or bowel problems, including ulcers or blockages
• Bladder or prostate problems, including a blockage or an enlarged prostate
• Thyroid problems 
• Heart disease
• High blood pressure

Other Medicines and Supplements. Diphenhydramine may interact with other medicines and supplements. Before using diphenhydramine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how diphenhydramine could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should use diphenhydramine while you are pregnant or trying to get pregnant.

Breastfeeding. Do not use diphenhydramine while you are breastfeeding. Diphenhydramine can pass into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

 

Interactions

Does diphenhydramine interact with foods or drinks?

There are no known interactions between diphenhydramine and foods or nonalcoholic drinks.

Do not drink alcohol while you are using diphenhydramine. The risk of drowsiness may be increased if you drink alcohol while using diphenhydramine.

Does diphenhydramine interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before using diphenhydramine.

• Any other medicine that contains diphenhydramine, including products applied to the skin that are used to relieve itching from insect bites and other skin problems
• Any other antihistamine, such as chlorpheniramine, which is a medicine commonly used to treat allergy symptoms
• A monoamine oxidase inhibitor (MAOI) within the past two weeks, which is a medicine usually used for depression or Parkinson’s disease
• Any other medicine that causes dizziness and sleepiness, such as prescription pain medicines, sleep medicines, and medicines for anxiety

This may not be a complete list of medicines that can interact with diphenhydramine. Always check with your health care provider.

Overdose/Missed Dose

What should I do if I accidentally use too much diphenhydramine?

If you or someone else has taken too much diphenhydramine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of diphenhydramine?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.

Sources

Look up another drug