Benadryl (Diphenhydramine)

Benadryl (diphenhydramine) is an over-the-counter drug classified as an antihistamine.

Histamine is a chemical created in the body that can cause symptoms like sneezing, itching eyes, and a runny nose in response to an allergen. It affects the airways and blood vessels, causing narrowing of the airways, rash, itchiness, and stomach cramps.

Histamine blockers like Benadryl prevent these unwanted side effects and work by blocking acetylcholinergic receptors, sodium channels, and inhibiting the reuptake of serotonin¹ (a neurotransmitter). This can cause drowsiness and other side effects such as dryness of the mouth.

Benadryl is an example of a first-generation antihistamine of the ethanolamine class.

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What is Benadryl used to treat?

Benadryl helps reduce the effects of natural chemicals in the body called histamines. It is used to treat the side effects of an allergic reaction, including:

  • Runny nose

  • Skin rash

  • Itching caused by insect bites

  • Watery eyes

  • Cold or allergy symptoms

  • Hives

Benadryl can be taken to relieve the symptoms of hayfever (seasonal allergies) and motion sickness. It can also be taken to induce sleep and treat certain symptoms of Parkinson's disease.

How do you take Benadryl?

Follow the directions on the label or prescription carefully and don’t take more than the recommended dose. Benadryl may only be taken for a short period of time until your symptoms clear up.

Benadryl dosage:

  • Adults and children aged 12 and over: 25–50mg (1–2 capsules)

  • Children aged six to 12: 12.5–25mg (1 capsule)

  • Children under six years of age: consult your doctor

Benadryl active ingredient

Benadryl has many different product names. Some of these products may contain just one ingredient, but others may contain two or more ingredients in combination with diphenhydramine.

  • Benadryl Allergy: diphenhydramine (an antihistamine)

  • Benadryl Allergy Plus Congestion: diphenhydramine and phenylephrine (a decongestant)

  • Benadryl Itch Stopping Cream: diphenhydramine and zinc (a skin protectant)

  • Benadryl Itch Cooling Gel: camphor (a type of pain reliever that’s applied to the skin)

When people say the word “Benadryl,” they usually refer to the products that contain diphenhydramine. Be careful when choosing which Benadryl products to buy or use because their ingredients may differ and it’s important to know exactly what the product contains.

How long before you see results?

You should start to feel relief within 15–30 minutes of taking Benadryl by mouth. You may need to take it several times throughout the day to get relief from your symptoms.

Potential side effects of Benadryl

If you experience these symptoms after taking Benadryl, get immediate medical help:

  • Hives

  • Difficulty breathing with a pounding heartbeat or a fluttering sensation in your chest

  • Swelling of your face, tongue, throat, or lips

  • Pain and irritation when urinating

  • Confusion

  • Feeling like you might faint

  • Tightness at the back of your head with uncontrollable tongue movements

Common adverse effects of Benadryl may include dizziness, dry mouth, nose, or eyes, constipation, an upset stomach, or a hangover feeling after using Benadryl at night.

This is not a comprehensive list of common side effects, and others may occur.

Contact your doctor if you experience any side effects.

Long-term use of Benadryl

Long-term use of Benadryl’s active ingredient, diphenhydramine, has been associated with an increased risk of developing dementia².

What happens if I miss a dose?

Since Benadryl is used when needed, you are unlikely to have a set dosing schedule.

If you're on a schedule, take your next scheduled dose at the usual time. If you miss a dose, skip the missed dose if you are scheduled to take your next dose soon. Don't take an extra dose to make up for the one you missed.

What happens if I overdose?

Taking too much Benadryl is unsafe, even though others may tell you otherwise. If you take too much, you may experience serious side effects, including abnormal heart rhythms (arrhythmias), hallucinations, and seizures, and it may cause death.

If you or someone close to you has taken too much Benadryl and is experiencing serious side effects, seek emergency medical attention immediately.

What to discuss with your doctor before taking Benadryl

Let your doctor know if you’re allergic to diphenhydramine, the active ingredient in Benadryl, or any other ingredients used in diphenhydramine preparations.

You should also advise your doctor of any other drug allergies you have.

Tell your doctor about any prescription and over-the-counter medications, vitamins, nutritional supplements, and herbal products you are currently taking or plan to take.

Tell your doctor if you have any of these conditions:

Tell your doctor if you’ve been told to follow a sodium-restricted diet if you intend to take Benadryl in liquid form.

Tell your doctor if you're pregnant, planning to get pregnant, or breastfeeding. If you become pregnant when taking Benadryl, tell your doctor.

Diphenhydramine should not generally be used by older adults, except to control serious allergic reactions, because they are not as safe or effective as other medications. Talk to your doctor if you're aged 65 or older before starting this medication.

If you’re having surgery, including dental procedures, tell the surgeon or dentist that you’re taking antihistamines.

If you have phenylketonuria (a rare, inherited condition that requires a special dietary regimen), be aware that some chewable tablets and rapidly dissolving tablets that contain diphenhydramine may be sweetened with aspartame, a source of phenylalanine.

Pregnancy and breastfeeding when taking Benadryl

Diphenhydramine can pass into breast milk and it may be harmful to a nursing baby. Antihistamines may also slow down breast milk production. Talk to your doctor before taking Benadryl if you're breastfeeding.

In some cases, it may be safe to use Benadryl during pregnancy, but it should not be used during the last two weeks of pregnancy as it increases the risk of eye disease in newborns.

Discuss Benadryl with your doctor before you decide to take it during pregnancy as they may advise against it and recommend a safer alternative.

Interactions with other drugs

Some medicines that interact with Benadryl may either decrease its effectiveness, affect how long it takes to work, increase side effects, and/or have less of an effect if taken with Benadryl.

In this case, Benadryl might not be suitable for you or you may need to stop taking one of your medications. Ask your doctor for advice about how to manage drug interactions.

Common medications that may interact with Benadryl include:

  • Benzodiazepines, such as diazepam, oxazepam, and temazepam

  • Monoamine oxidase inhibitors, such as isocarboxazid, selegiline, or tranylcypromine

  • Opioids, such as oxycodone, morphine, or codeine

  • Sedatives, or any medication that causes sedation, such as sleeping pills, muscle relaxants, or antidepressants

  • Other medications that contain diphenhydramine, such as creams and gels

  • Other medications used to treat allergies

Tips and advice for taking Benadryl

Do not give Benadryl to children under the age of two and do not use it to make children feel sleepy.

If you're prone to motion sickness, take Benadryl 30 minutes before you enter a situation that may cause you to feel sick (like a long car ride, a plane or boat trip, or amusement park rides). Take Benadryl before a meal and at bedtime for as long as you have motion ­sickness.

Take Benadryl 30 minutes before bedtime to help you fall asleep.

Talk to your doctor if your symptoms don’t get better after seven days of treatment or if you have a high fever, headache, cough, or skin rash.

Be aware that this medication makes you sleepy. Don't drive a car or operate any machinery until you know how the medication affects you. Don't drink alcohol while taking this medication, as it can make you feel more sleepy.

Common questions about Benadryl

Here are answers to some frequently asked questions about Benadryl.

Does Benadryl make you sleepy?

Yes, Benadryl causes drowsiness in most people who take it. This side effect may disappear after three to four days of use.

Can Benadryl help with anxiety?

Benadryl is not an effective treatment for anxiety and it shouldn’t be used in this way.

Since sleepiness is a side effect of Benadryl, you might assume it would help you relax and ease your anxiety symptoms, but sleepiness usually goes away after you have been taking Benadryl for a few days.

Is Benadryl an NSAID?

No, Benadryl is not an NSAID (nonsteroidal anti-inflammatory drug); Benadryl is an antihistamine.

Can Benadryl be used as an expectorant?

Benadryl doesn't work as an expectorant. An expectorant helps loosen mucus in your respiratory tract so you can cough it out.

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Here at HealthMatch, we’ve done our best to ensure that the information provided in this article is helpful, up to date, and, most importantly, accurate.

However, we can’t replace the one-to-one advice of a qualified medical practitioner or outline all of the possible risks associated with this particular drug and your circumstances.

It is therefore important for you to note that the information contained in this article does not constitute professional medical or healthcare advice, diagnosis or recommendation of treatment and is not intended to, nor should be used to, replace professional medical advice. This article may not always be up to date and is not exhaustive of all of the risks and considerations relevant to this particular drug. In no circumstances should this article be relied upon without independent consideration and confirmation by a qualified medical practitioner.

Your doctor will be able to explain all possible uses, dosages, precautions, interactions with other drugs, and other potential adverse effects, and you should always talk to them about any kind of medication you are taking, thinking about taking or wanting to stop taking.

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