Diphenhydramine Side Effects in Older or Elderly People

Over-the-counter sleep aids, especially those that contain diphenhydramine (like Benadryl), are a relatively common choice for people with insomnia.

However, older people shouldn't use medicines containing diphenhydramine, as they may be prone to dangerous side effects, including:

  • Confusion
  • Dementia
  • Urinary retention
  • Dizziness
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What Is Diphenhydramine?

Diphenhydramine is the most common ingredient found in over-the-counter sleeping pills.

It's the main ingredient in Benadryl, which is an allergy medication that causes sleepiness as a side effect. It's therefore commonly used in “PM” preparations for insomnia, including:

Like doxylamine, a related sleeping pill ingredient in Nyquil and Unisom, diphenhydramine is an antihistamine. It inhibits histamine pathways in the brain. Histamines enhance wakefulness, so medications that block histamine pathways can cause sleepiness.

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 (called 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 and about half of it is removed in between four and eight hours.

Nevertheless, morning side effects such as residual sleepiness or hangover can occur, though this typically improved after about four nights of use.

In a study of older adults, diphenhydramine reduced awakenings but didn't improve sleep latency, total sleep time, or sleep quality.

Serious Side Effects

Evidence suggests diphenhydramine may result in serious side effects in older adults—those over 65. These effects may lead you to think twice about using it. 

The older you are, the greater the risk of adverse effects. These are in addition to the side effects everyone else can experience.

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.

Cognition and Drying

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

One of the more significant 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 be associated with the long-term development of dementia.

There may also be “drying effects.” These may manifest as dry mouth, constipation, blurred vision, and urinary retention. Urinary retention may increase the risk of developing urinary tract infections (UTIs) or affect kidney function.

Contraindications

Older people should not use diphenhydramine if they have a history of:

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, and this may help to relieve the awakenings and resulting insomnia.

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