What to Know About Diphenhydramine

An Antihistamine Drug Commonly Used for Allergic Reactions

Diphenhydramine is a first-generation antihistamine that reduces the naturally occurring effects of histamine in the body. An increase in histamine release generally occurs as a direct reaction to a chemical, drug, or other allergen, especially in allergic reactions.

Diphenhydramine is a common ingredient that is used in a variety of over-the-counter (OTC) medications that can be used in a variety of forms, including single-ingredient and combination-ingredient products, and as pills, capsules, liquids, and chewable tablets. The most common brand name is Benadryl.

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Uses

Diphenhydramine is most commonly used to treat allergic symptoms caused by histamine release. It is also used for the following purposes:

Off-Label Uses

These are uses that are not indicated for medication by the Food and Drug Administration (FDA), but a doctor may recommend using it nonetheless:

Before Taking

Your medical provider will help determine the dose of the medication and when you should take it. It is important to note that diphenhydramine is an over-the-counter medication and safe dosing is found on all generic and brands of this medication.

Diphenhydramine is considered a first-line treatment for FDA approved uses. Off-label uses are options only after the first-line option has failed.

The following guidelines may be useful to help you understand some specifics as to how to take diphenhydramine: 

  • Inform all healthcare providers that you are taking this drug.
  • Diphenhydramine can be administered via tablet, liquid, and/or intravenously.
  • Chewable tablets and oral-disintegrating tablets should be chewed well or let them dissolve completely in the mouth.
  • Diphenhydramine can be taken with or without food.
  • Diphenhydramine is taken as needed.
  • Take the medication dosage as ordered from a medical provider or as indicated on the packaging.
  • Avoid driving or operating heavy machinery until you are aware of how the medication will affect you.
  • Avoid drinking alcohol while taking diphenhydramine.
  • Talk with your healthcare provider before the use of marijuana, or prescription and over-the-counter drugs that may slow your actions.
  • Do not take if you are pregnant or breastfeeding until after speaking to your healthcare provider.
  • Do not take with other medications containing diphenhydramine.

Talk to your doctor about all medications, supplements, and vitamins that you currently take. While some drugs pose minor interaction risks, others may outright contraindicate use or prompt careful consideration as to whether the pros of treatment outweigh the cons in your case.

Other Antihistamines

Diphenhydramine is one of the first generation antihistamines, which are known to be sedating. Others include brompheniramine, chlorpheniramine, dimenhydrinate, and doxylamine.

Second-generation antihistamines are now generally preferred because they are non-sedating. These include Alavert and Claritin (loratadine), Zyrtec (cetriizine) and Allegra (fexofenadine).

Dosage 

All listed dosages are according to the drug manufacturer. Check your prescription and talk to your doctor to make sure you are taking the right dose for you.

General Adult Dosage Information

These dosages are suggested by the manufacturer:

  • Extrapyramidal reaction: 25 to 50 milligrams (mg) orally 3 to 4 times a day
  • Insomnia: 50 mg orally once a day at bedtime
  • Motion sickness: 25 to 50 mg 3 to 4 times a day
  • Allergic rhinitis: 25 to 50 mg orally every 4 to 6 hours as needed Maximum dose: 300 mg/day
  • Cold symptoms: 25 to 50 mg orally every 4 to 6 hours as needed. Maximum dose: 300 mg/day
  • Pruritus: 25 to 50 mg orally every 4 to 6 hours as needed. Maximum dose: 300 mg/day
  • Urticaria: 25 to 50 mg orally every 4 to 6 hours as needed. Maximum dose: 300 mg/day

Pediatric Dosage Information

There are many formulations of products that contain diphenhydramine for children, but it is important to note the age restrictions and recommended dosages. These are examples.

Children's BENADRYL Allergy Liquid (diphenhydramine hydrochloride 12.5 mg in 5 mL)
Age Dose
Children under 2 years Do not use
Children 2 years to 5 years Do not use unless directed by healthcare provider
Children 6 years to 11 years 5 ml to 10 ml
Children's BENADRYL Allergy Plus Congestion (diphenhydramine hydrochloride 12.5 mg and phenylephrine hydrochloride 5 mg in 5 mL)
Age Dose
Children under 4 years Do not use
Children 4 years to 5 years Do not use unless directed by healthcare provider
Children 6 years to 11 years 5 ml
Adults and children 12 years and over 10 ml
Children's BENADRYL Chewable Tablets (diphenhydramine hydrochloride 12.5 mg)
Age Dose
Children under 2 years Do not use
Children 2 years to 5 years Do not use unless directed by a healthcare provider
Children 6 years to 11 years 1 to 2 chewable tablets
Adults and children 12 years and over 2 to 4 chewable tablets

How To Take and Store

Follow these precautions:

  • Store at room temperature and protected from light.
  • Store in a dry place.
  • Do not refrigerate or freeze.
  • Throw away liquid suspension after eight weeks due to potential instability.
  • Throw away unused or expired medication.

Side Effects

There may be some side effects associated with the administration of diphenhydramine, which can be common or more severe. Most side effects associated with this medication are not harmful but all side effects should be reported to your healthcare provider.

More common side effects can include:

  • Sedation/sleepiness
  • Dizziness
  • Epigastric distress
  • Thickening of secretions
  • Headache
  • Incoordination
  • Dry mouth
  • Vertigo
  • Urticaria
  • Irritability
  • Euphoria

Serious side effects, which should be immediately reported to your physician, include: 

Warnings and Interactions

Diphenhydramine or any medications containing it should not be used by adults age 65 or older unless your doctor determines that the benefits outweigh the risks. There are usually other medications that are safer and more effective.

Diphenhydramine should only be used with caution by people to whom any of the following may apply, so check with your doctor before using:

 

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Article Sources
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  5. MedlinePlus. Diphenhydramine. Updated August 15, 2018.