Benadryl: Side Effects and Cautions

Benadryl (diphenhydramine) is a well-known antihistamine used to treat allergy symptoms including sneezing, runny nose, and itchy and watery eyes, as well as colds, dry coughs, insomnia, and motion sickness. While typically mild, the side effects of Benadryl may be more intense for some people—making using the drug undesirable, especially during the day, or even unsafe.

General Side Effects

Sold over-the-counter without a prescription since 1946, Benadryl now comes as a tablet, rapid-dissolving tablet or strip, capsule, liquid capsule, powder, and liquid. A short-acting antihistamine, Benadryl lasts four to six hours.

Generally considered a safe and effective medication, it is not without side effects.

If these common side effects are severe or bothersome, talk to your doctor:

  • Dry mouth, nose, and throat
  • Drowsiness
  • Dizziness
  • Nausea or vomiting
  • Loss of appetite
  • Constipation
  • Increased chest congestion
  • Headache
  • Muscle weakness
  • Excitability (especially in children)
  • Nervousness

Benadryl can impair mental and motor functioning, as well as your performance at work or school. It can also impair a person’s ability to operate a motor vehicle or other potentially dangerous equipment.

Serious Side Effects

Call your doctor immediately if you experience any of these more serious side effects of Benadryl:

  • Vision problems
  • Difficulty urinating or painful urination

While these side effects can be experienced by anyone on Benadryl, the drug should particularly be used with caution in people taking certain medications and those in specific populations.

Interactions

Benadryl may interact with medications used for treating health conditions including:

  • Blood-pressure drugs Qbrelis, Prinivil, and Zestril (lisinopril),
  • Antidepressants Desyrel (trazodone) and Zoloft (sertraline)
  • Antianxiety medication Xanax (alprazolam)
  • Opioid pain reliever hydrocodone
  • Seizure medicine Neurontin (gabapentin)

Do not mix alcohol with Benadryl as it may increase side effects and add to the drowsiness caused by this medication.

Special Considerations

Use of Benadryl in particular individuals can result in amplified side effects, risk of overdose, and other concerns. It's imperative that you check with a doctor before using this medication if you (or someone you care for) are in any of the following groups.

People With Certain Health Conditions

Benadryl works to relieve congestion by drying out nasal passages. While this may be beneficial if you have allergies, the medication can also dehydrate the entire body. This can alter your heart rate, blood pressure, respiration, and elimination.

Given this, people with certain health conditions should not use Benadryl unless under the supervision of a doctor. The antihistamine may exacerbate underlying health concerns, including: 

Your doctor can best guide you in determining if Benadryl is safe for you.

Children

Benadryl and other first-generation antihistamines should be used with caution in children and preferably under the direction of a physician. Benadryl should never be given to a child for the purpose of making them sleepy.

Children may experience similar side effects as adults, or potentially experience unexpected side effects such as excitement, irritability, and insomnia.

The potential for overdose is a major concern in young children, as it can lead to seizures and problems with heart rate.

Signs of Benadryl overdose include:

  • Blurred vision
  • Very dry eyes
  • Enlarged pupils
  • Dry mouth
  • Ringing in the ear (tinnitus)
  • Dry, red skin
  • Nausea or vomiting
  • Drowsiness or increased sleepiness
  • Inability to urinate
  • Low blood pressure
  • Rapid heartbeat
  • Unsteadiness
  • Nervousness
  • Agitation, confusion, delirium, or hallucinations
  • Tremor
  • Seizures
  • Depression

In case of overdose, call the poison control helpline at 1-800-222-1222 or visit the poison control website for more information. Call 911 if the person has collapsed, had a seizure, has trouble breathing, or can't be awakened.

Older Adults

Benadryl is not recommended for adults ages 65 and older, except to treat an acute allergic reaction. Older adults may be more affected by side effects than younger adults.

Common side effects such as sleepiness, dizziness, and decreased reaction times may be more pronounced in older adults, especially if they have other medical conditions, and may result in falls or accidents. 

Because of Benadryl's dehydrating effects, it may cause dry mouth, constipation, blurred vision, and urinary retention, which can increase the risk of developing urinary tract infections (UTIs) or affect kidney function.

In addition, antihistamines like Benadryl can have anticholinergic effects, which can lead to cognitive impairment or confusion. There is growing evidence that chronic use of these medications may be associated with the long-term development of dementia.

Pregnant and Nursing Women

Benadryl is a commonly used antihistamine during pregnancy, especially because it has a pregnancy category B rating. That said, it should not be considered as a preferred antihistamine for routine use in pregnant or breastfeeding women. Regardless of how often one plans to take it, the drug should only be used under the direction of a physician.

Large doses or overdoses of Benadryl can result in premature contractions during pregnancy. Caution should be used when giving Benadryl near delivery, as the side effects in a newborn can include excitement, irritability, and seizures.

Like many other medications, Benadryl is secreted in breast milk and may be passed to a nursing child, causing temporary side effects such as irritability and colic.

Second-generation antihistamines, such as Zyrtec (cetirizine) or Claritin (loratadine), have fewer side effects, are more effective, and are safer medications for pregnant women and nursing children.

A Word From Verywell

Benadryl is an effective antihistamine, however, its side effects make it less desirable or contraindicated for some. Newer antihistamines such as Xyzal (levocetirizine), Zyrtec (cetirizine), Allegra (fexofenadine), Claritan (loratadine), and Clarinex (desloratadine) do not typically cause drowsiness and may be preferred for longterm use over Benadryl. Talk to your doctor about your allergy symptoms for recommendations on the best antihistamine for you.

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