May 25, 2023

What Is Benadryl and What Does Benadryl Do?

Benadryl (diphenhydramine) is an antihistamine. That means it reduces the action of immune system chemicals called histamines. These substances cause sneezing, watery eyes, and a runny nose as part of the body’s defenses against pathogens. 

While those reactions are essential, sometimes they’re excessive. Benadryl can help tone them down. 

Benadryl is also used to prevent and treat motion sickness, treat insomnia in adults, treat bee sting allergies, and help control some conditions that cause abnormal movements, such as early-stage Parkinsonian syndrome. 

Important note: You should never give Benadryl to a child under age two or any child to make them sleepy. 

Before Taking Benadryl

Some people should avoid taking Benadryl. If you’ve never taken it, you should talk with your doctor if you have any of the following health conditions:

  • Liver or kidney disease
  • Breathing disorders like asthma or chronic obstructive pulmonary disease (COPD)
  • Cough with mucus
  • Heart disease
  • Thyroid disorder
  • Low blood pressure
  • Cough caused by chronic bronchitis, emphysema, or smoking
  • Digestive tract blockage
  • Colostomy or ileostomy
  • Urination problems or bladder obstruction
  • Glaucoma
  • Conditions treated by taking potassium

If you’re pregnant or nursing, you should also talk with your doctor before taking Benadryl.

How Long Does Benadryl Take to Work?

People using Benadryl typically notice effects within 30 minutes. So, if you’re taking it for motion sickness or insomnia, you should plan accordingly. 

Benadryl Side Effects

Does Benadryl make you sleepy or cause other side effects? Yes, it can. In addition to drowsiness, these are some of the side effects common with Benadryl:

  • Dizziness
  • Loss of coordination
  • Dry mouth, eyes, throat, or nose
  • Upset stomach
  • Constipation
  • Blurred vision
  • "Hangover" sensation following nighttime use

Older adults are more likely to experience Benadryl side effects. 

Get emergency medical help if you experience signs of an allergic reaction to Benadryl, including: 

  • Trouble breathing
  • Hives
  • Swelling of your throat, lips, tongue, or face

Stop taking Benadryl and contact your doctor if you experience any of the following:

  • Changes in urination, including little or no urine output, trouble urinating, or painful urination
  • Fluttering sensation in your chest
  • Pounding heartbeat
  • Confusion
  • Feeling like you might lose consciousness
  • Neck or jaw tightness
  • Uncontrollable movements of your tongue

Because Benadryl can cause symptoms like sleepiness and loss of coordination, you should avoid driving or using dangerous machinery or tools until you understand how the medication affects you. Also, drinking alcohol while taking Benadryl can intensify some side effects.

Benadryl can also cause photosensitivity, meaning it increases the effects of exposure to sunlight. 

Drug Interactions with Benadryl

Taking Benadryl with other prescription or over-the-counter medications, herbal products, or vitamins can cause harmful side effects. Talk with your doctor about potential interactions. 

It’s crucial to ask your doctor whether you can use Benadryl if you take sleeping pills, muscle relaxers, pain medication, or medicine for seizures, depression, or anxiety.

What’s the Appropriate Benadryl Dosage?

You should take Benadryl exactly as directed by your doctor or the instructions on the package. 

Be aware that certain combination medications contain antihistamines, so you should carefully read the labels on all over-the-counter and prescription drugs to ensure you get the proper dosage across all medicines you take. 

If you overdose on Benadryl or similar medications, get emergency medical care.

Talk with Your Doctor About Taking Benadryl

Benadryl is a generally safe and effective medication that can treat allergies and other health conditions. Just be sure to talk with your doctor or pharmacist about side effects and drug interactions before you start taking it. 

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