What Happens If You Take Benadryl Before Bed Every Night, Doctors Say

Here's why you may not want to use it as a long-term sleep aid.

Benadryl is a common over-the-counter (OTC) antihistamine used to treat allergies, the common cold, hay fever, and itchy skin—but its active ingredient, diphenhydramine, is also known to cause drowsiness.

"Diphenhydramine blocks the effects of histamine in your brain and this reduces symptoms. It enters the brain in large quantities and this can make you feel drowsy," explains the U.K.'s National Health Services (NHS). "Diphenhydramine also blocks the effects of another chemical called acetylcholine," a neurotransmitter that excites the brain's nerve cells.

Because of this, some people use Benadryl as an off-label sleep aid. However, many experts caution against using antihistamines to help you fall asleep, especially on a nightly basis. Read on to learn what happens if you take Benadryl before bed every night—including some serious side effects that could put you in harm's way.

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You may be drowsy during the day.

Young woman is waking up and looking at her smart phone.
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Benadryl does indeed make you sleepy, but using it as a sleep aid may not go exactly as planned. According to James Walker, MD, a physician and contracted medical advisor for Welzo, that's because Benadryl causes "significant sedation and drowsiness, which may persist into the following day. This can interfere with daily activities."

It's especially important to avoid driving or operating heavy machinery while taking Benadryl, adds Poison Control. "Benadryl can impair your hand-eye coordination and reaction time due to sleepiness," making serious accidents more likely, their experts warn.

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You may be at greater risk of dementia.

A senior woman sitting on the couch with a confused look on her face
iStock / Armand Burger

Another potential side effect of taking Benadryl on a nightly basis is that it can lead to cognitive decline. In fact, a 2015 report published in the journal JAMA Internal Medicine concluded that people who took Benadryl or a similar anticholinergic medication for three years or more had a 54 percent higher dementia risk, compared with those taking the medication for three months or less.

"Benadryl can impair cognitive function, including memory and attention. It can lead to difficulty concentrating and performing tasks that require mental alertness," warns Walker.

You may increase your fall risk.

Senior man fall risk falling in living room
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If you take Benadryl every night as a sleep aid, you may also be at higher risk of falling. "Benadryl can affect balance and coordination, making individuals more prone to falls, especially in older adults. This risk is further increased when combined with other sedating substances like alcohol," says Walker.

In fact, Harvard Medical School listed Benadryl as one of the medications most likely to raise your fall risk. "Medications that suppress the central nervous system are among those most likely to contribute to falling, as they reduce alertness and cause slower reactions and movements," their experts explain.

You may experience urinary retention.

Woman holding her bladder in pain
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Prolonged use of Benadryl is also known to cause certain bladder problems, Walker warns. In particular, he says this type of antihistamine can cause urinary retention, which makes it difficult to empty the bladder completely. "This can be especially concerning for individuals with pre-existing urinary issues or prostate enlargement," he tells Best Life.

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You may develop a drug interaction.

Prescription pills that are blue.
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Finally, using Benadryl as a nightly sleep aid can cause harm to your health if you take certain other medications. Specifically, Walker notes that Benadryl may interact dangerously with sedatives, tranquilizers, and certain antidepressants. "These interactions can intensify the sedative effects and increase the risk of adverse reactions," he says.

Instead of opting for a nightly Benadryl, Walker suggests speaking with your doctor to determine what's causing your insomnia. "It is crucial to remember that the use of Benadryl or any other medication for sleep aid should be temporary and under the guidance of a healthcare professional," he says. "Chronic insomnia or persistent sleep difficulties should be evaluated by a healthcare provider to identify and address any underlying causes or conditions."

Best Life offers the most up-to-date information from top experts, new research, and health agencies, but our content is not meant to be a substitute for professional guidance. When it comes to the medication you're taking or any other health questions you have, always consult your healthcare provider directly.

Lauren Gray
Lauren Gray is a New York-based writer, editor, and consultant. Read more
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