Diphenhydramine belongs to a group of medications known as antihistamines. Antihistamines are used to treat symptoms caused by allergies, including itchy and watery eyes, sneezing, runny nose, and skin rash and irritations.

The cream form of this medication is used for the relief of swelling and itching caused by insect bites, poison ivy, poison oak, mild cases of sunburn, and other minor skin irritations.

This medication works by blocking the effects of histamine, a substance released by the body involved in allergies. It usually starts to work within one hour.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are using this medication, speak to your doctor or pharmacist.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to use this medication if their doctor or pharmacist has not recommended it.

Adults and children 12 years of age and older: The usual dose is 25 mg to 50 mg taken by mouth 3 or 4 times a day. No more than 300 mg should be taken in a 24-hour period. As there are various strengths and forms of diphenhydramine, talk to your doctor or pharmacist before taking this medication. Take diphenhydramine exactly as directed by your doctor or pharmacist.

Children: The dose of diphenhydramine for children varies based on age and body weight. Always read the label on the product you have to ensure the correct dose. If you are not sure, ask your health care professional to calculate the dose. This medication should not be used for children under the age of 2 years unless recommended by your physician.

Do not give diphenhydramine capsules or caplets to children younger than 12 years of age unless directed to do so by your child's doctor. As there are various strengths and forms (e.g., children's liquid, elixir) of diphenhydramine, talk to your doctor or pharmacist before giving this medication to a child.

Use an oral syringe to measure each dose of the liquid, as it gives a more accurate measurement than household teaspoons.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones above, do not change the way that you are using the medication without consulting your doctor.

It is important to use this medication exactly as recommended by your doctor or pharmacist.

Store this medication at room temperature and keep it out of the reach of children.

Tablets
This medication is available as a 25 mg tablet.

Capsules
This medication is available as a 25 mg capsule.

Liquid Capsules
This medication is available as a 50 mg liquid capsule.

Extra Strength Tablet
This medication is available as a 50 mg tablet.

Do not use this medication if you are allergic to diphenhydramine or any ingredients of the medication.

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is used in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who uses this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people using this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• constipation
• dry mouth
• drowsiness
• dizziness
• excitation (especially in children)
• nausea
• nervousness
• restlessness
• ringing in the ears
• thickening of mucus
• trouble sleeping

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• blurred vision or any change in vision
• confusion or difficulty concentrating
• difficult or painful urination
• rapid or pounding heartbeat

Stop taking this medication and seek immediate medical attention if any of the following occur:

• symptoms of a severe allergic reaction (e.g., hives; difficulty breathing; swelling of the face, mouth, tongue, or throat)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Asthma or breathing problems: Diphenhydramine can cause the secretions produced in the lungs to become thick and difficult to clear out of the lungs. If you have breathing problems such as asthma or chronic obstructive pulmonary disease (COPD), discuss with your doctor discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Drowsiness/reduced alertness: This medication can cause drowsiness. Avoid driving or operating machinery until you have determined that this medication does not affect your ability to perform these tasks safely.

Glaucoma: This medication may cause the symptoms of glaucoma (increased pressure in the eye) to become worse. If you have glaucoma, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Report any changes in vision to your doctor as soon as possible while you are taking this medication.

Heart disease:Although not common, diphenhydramine can cause changes to heart rhythm and blood pressure. If you have any heart conditions ask your health care professional if any special monitoring is required.

Stomach ulcers: This medication may make the symptoms of stomach ulcers worse. If you have stomach problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Thyroid disease: If you have thyroid disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Urinary tract problems: This medication can make passing urine more difficult, increasing the symptoms of an enlarged prostate gland or other urinary tract problems. If you have prostate problems or difficulty passing urine, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: The safety of using this medication while breast-feeding has not been established. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: Children are at an increased risk of overdose and side effects from this medication. Antihistamines such as diphenhydramine can cause excitation in young children. This medication should not be used in children under the age of 2 years unless under the advice of a physician.

Seniors: If you are a senior, this medication may be more likely to cause dizziness, drowsiness, and low blood pressure. Talk to your doctor or pharmacist before taking this medication.

There may be an interaction between diphenhydramine and any of the following:

• aclidinium
• alcohol
• alfuzosin
• amantadine
• amiodarone
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• atropine
• barbiturates (e.g., butalbital, pentobarbital, phenobarbital)
• benzodiazepines (e.g., alprazolam, diazepam, lorazepam)
• benztropine
• betahistine
• botulinum toxin
• brimonidine
• buprenorphine
• buspirone
• cannabis
• chloral hydrate
• darifenacin
• disopyramide
• domperidone
• donepezil
• dronedarone
• efavirenz
• eluxadoline
• esketamine
• fesoterodine
• flavoxate
• flunarizine
• galantamine
• glucagon
• glycopyrrolate
• ipratropium
• ketotifen
• lemborexant
• lopinavir
• methadone
• methylphenidate
• metoclopramide
• mirabegron
• mirtazapine
• monoamine oxidase inhibitors (MAOIs; e.g., moclobemide, phenelzine, rasagiline, selegiline, tranylcypromine)
• muscle relaxants (e.g., baclofen, cyclobenzaprine, methocarbamol, orphenadrine, tizanidine)
• nabilone
• narcotic pain relievers (e.g., codeine, fentanyl, morphine, oxycodone, tapentadol, tramadol)
• nitroglycerin
• other antihistamines (e.g., azelastine, cetirizine, doxylamine, hydroxyzine, loratadine)
• oxybutynin
• pitolisant
• potassium supplements (e.g., potassium chloride, salt substitutes that contain potassium)
• pramipexole
• pregabalin
• procainamide
• quinidine
• rivastigmine
• ropinirole
• rotigotine
• saquinavir
• scopolamine
• seizure medications (e.g., clobazam, carbamazepine, levetiracetam, phenobarbital, phenytoin, primidone, rufinamide, topiramate, valproic acid, zonisamide)
• solifenacin
• tetrabenazine
• thalidomide
• thiazide diuretics (water pills; e.g., hydrochlorothiazide, indapamide, metolazone)
• tiotropium
• tolterodine
• trazodone
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
• trospium
• umeclidinium
• valerian
• zolpidem
• zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.