Diphenhydramine Side Effects in Older or Elderly People

Diphenhydramine is a common ingredient in sleeping aids; it is also used to treat allergies. While effective, the risk of serious diphenhydramine side effects—including confusion, dizziness, urinary retention, and liver or kidney issues—is increased in people age 65 and older.

This article explores how diphenhydramine works, potential side effects, and why it's generally recommended that older adults avoid using diphenhydramine except to manage allergic reactions.

What Is Diphenhydramine?

Diphenhydramine is an antihistamine. Histamines are chemicals naturally produced by the body that enhance wakefulness. Diphenhydramine blocks h1 receptors, histamine pathways in the brain that are crucial for these wake-promoting effects. In doing so, diphenhydramine can cause sleepiness.

This effect is beneficial for those who turn to over-the-counter sleeping pills to treat insomnia. Diphenhydramine is commonly used in “PM” medication preparations as well, including:

• Tylenol PM
• Advil PM
• ZzzQuil

Diphenhydramine is also the main ingredient in Benadryl. In this case, though, the sleepiness effect is considered a downside of using the drug to tame allergy symptoms.

More than half of all over-the-counter sleep aids contain medications that block H1 receptors, such as diphenhydramine or doxylamine (found in Nyquil and Unisom).

Diphenhydramine for Insomnia

The efficacy of diphenhydramine as a sleep aid is not well studied. There's some evidence that, when used over the short term (less than two weeks), diphenhydramine may help you stay asleep.

This is sometimes measured with a concept called sleep efficiency. Sleep efficiency is the total amount of sleep divided by the total amount of time spent in bed. As reported by people who use the medication, it seems to improve.

The time it takes to fall asleep (sleep latency) or the total amount of time spent sleeping do not seem to similarly improve. This may relate to the time it takes for the medication to start working and how long it stays in the body.

In general, diphenhydramine is active for between four and six hours. Nevertheless, morning side effects such as residual sleepiness or hangover can occur.

Diphenhydramine Side Effects

Evidence suggests diphenhydramine may result in serious side effects in adults ages 65 and older. These are in addition to the side effects everyone else can experience. The older you are, the greater the risk of adverse effects.

Fall Risk

Diphenhydramine can cause decreased reaction times and dizziness.

In older people with other medical problems or physical impairments, this may lead to falls or accidents, especially while getting up to urinate at night. The potential for bone fractures is a notable concern.

Cognitive Impairment and Dementia

Antihistamines like diphenhydramine can have anticholinergic effects as well. This means that the medication acts on the signaling chemical called acetylcholine, which can have important consequences.

One of the more significant ones is cognitive impairment, such as confusion, that's similar to what occurs with dementia or delirium.

Growing evidence suggests chronic use of these medications may also be associated with the long-term development of dementia.

Drying Effects

There may also be “drying effects.” These may manifest as:

• Dry mouth
• Constipation
• Blurred vision
• Urinary retention

Urinary retention may increase the risk of developing urinary tract infections (UTIs) or affect kidney function.

Contraindications

Diphenhydramine can be especially dangerous and should not be used for any reason by older adults with history of:

• Closed-angle glaucoma
• Constipation
• Urinary retention
• Asthma
• Severe liver disease

Summary

The older you are, the greater the risk of adverse effects from diphenhydramine. It generally should not be used as a sleep aid in those ages 65 and older.

A Word From Verywell

Fortunately, other treatment options are available for insomnia in older adults.

While sleeping pills are one option, cognitive behavioral therapy for insomnia (CBTI) may be the best option without the risk of any medication side effects.

When present, obstructive sleep apnea should be identified and treated. This may help reduce awakenings and resulting insomnia.