Diphenhydramine Side Effects in Older or Elderly People

Shot of a mature businesswoman working from her home office

 TinPixels / Getty Images

The difficulties falling or staying asleep that occur with insomnia may lead many people to find a solution in the pharmacy aisles. The use of over-the-counter sleep aids, especially those that contain diphenhydramine (like Benadryl), is relatively common. However, there are some reasons why older people and the elderly should not use medicines containing diphenhydramine to aid sleep. Learn why older people should skip the use of sleeping pills that contain the substance due to the risks of side effects like confusion, dementia, urinary retention, and dizziness.

What Is Diphenhydramine in Benadryl and "PM" Sleeping Pills?

Diphenhydramine is the most common ingredient found in over-the-counter sleeping pills. It is the main ingredient in Benadryl, and it causes sleepiness as a side effect. It is therefore commonly incorporated into “PM” preparations used to treat insomnia, including: Tylenol PM, Advil PM, and ZzzQuil.

Like doxylamine, a related sleeping pill ingredient in Nyquil and Unisom, diphenhydramine is an antihistamine medication. It can be helpful to relieve allergic responses. It also inhibits histaminergic pathways in the brain. These are pathways that extend from the brainstem to the rest of the brain. They enhance wakefulness. Therefore, medications that block the pathways can cause sleepiness.

Does Diphenhydramine Work Well to Treat Insomnia?

The efficacy of diphenhydramine is not well studied. There is some evidence that, when used over the short term (less than 2 weeks), diphenhydramine may improve sleep continuity. In other words, there seem to be fewer awakenings at night. 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 4-6 hours and about half of it is removed in 4-8 hours. Nevertheless, morning side effects such as residual sleepiness or hangover can occur, though this typically improved after about 4 days of nightly use.

In a study of older adults, a trial comparing the use of temazepam (Restoril) and diphenhydramine showed a reduction in awakenings but not in sleep latency, total sleep time, or sleep quality with the use of diphenhydramine. An important consideration in this population is the risk of serious side effects.

Serious Side Effects With Diphenhydramine Include Dementia

There is evidence that the use of diphenhydramine among older adults or the elderly may result in serious side effects. These effects may lead you to think twice about its use. 

First, who is considered to be an older adult? In general, this includes people who are older than age 65.

The older a person becomes, the greater the risk of adverse effects. Older adults are subject to the same side effects as everyone else, but they also may experience additional problems.

Diphenhydramine causes a handful of common side effects that include sleepiness and decreased reaction times. It may also cause dizziness. Among older people with other medical problems or physical impairments, this may lead to falls or accidents. This is more likely if the person is waking to urinate at night and gets up.

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 may occur with dementia or delirium. This may be identified as confusion. There is growing evidence that chronic use of these medications may be associated with the long-term development of dementia.

There may also be “drying effects” as a result. 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.

Older people should not use diphenhydramine if they have a history of closed-angle glaucoma, constipation, urinary retention, asthma, or severe liver disease. There may be long-term effects on memory that increase the risk of dementia. Given the risk of other serious side effects that affect thinking and balance, it may be important to avoid diphenhydramine use generally.

A Word From Verywell

Fortunately, there are other treatment options available for insomnia in older adults and the elderly. Additional sleeping pills can be used, but 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.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Glass JR, Sproule BA, Herrmann N, Busto UE. Effects of 2-week treatment with temazepam and diphenhydramine in elderly insomniacs: a randomized, placebo-controlled trial. J Clin Psychopharmacol. 2008;28(2):182-188. doi:10.1097/JCP.0b013e31816a9e4f

  2. Verster JC, de Weert AM, Bijtjes SIR, et al. Driving ability after acute and sub-chronic administration of levocetirizine and diphenhydramine: a randomized, double-blind, placebo-controlled trial. Psychopharmacology. 2003;169(1):84-90. doi:10.1007/s00213-003-1462-6

  3. American Geriatrics Society 2019 Updated AGS Beers Criteria® for Potentially Inappropriate Medication Use in Older Adults. J Am Geriatr Soc. 2019;67(4):674-694. doi:10.1111/jgs.15767

  4. Gray SL, Anderson ML, Dublin S, et al. Cumulative use of strong anticholinergics and incident dementia: a prospective cohort study. JAMA Intern Med. 2015;175(3):401-407. doi:10.1001/jamainternmed.2014.7663

  5. McMillan JM, Aitken E, Holroyd-Leduc JM. Management of insomnia and long-term use of sedative-hypnotic drugs in older patients. CMAJ. 2013;185(17):1499-1505. doi:10.1503/cmaj.130025

  6. Diphenhydramine. In: LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Bethesda, MD: National Institute of Diabetes and Digestive and Kidney Diseases; 2017.

Additional Reading
Related Articles