Sleep research review
Is It Safe to Take Diphenhydramine (Benadryl) Every Night for Sleep? A Research Review
Diphenhydramine can make people sleepy, but the evidence does not support making it a regular, long-term treatment for insomnia. Short-term studies show limited sleep benefits, while tolerance, next-day impairment and anticholinergic side effects complicate nightly use. This does not mean every occasional dose is unsafe. It means that a medicine’s ability to cause drowsiness should not be mistaken for proof of lasting benefit or long-term safety.[2–5,7]
What is being used for sleep
Diphenhydramine is a sedating antihistamine. In the United States, Benadryl Allergy products containing it are labeled for allergy and certain cold symptoms. Separate diphenhydramine sleep-aid products are labeled for occasional sleeplessness. Those are different intended uses, even though the active ingredient is the same. The Drug Facts panel, rather than the brand name alone, identifies what a particular product contains and is intended to treat.[1,6]
The sleep-aid label’s warning to stop use and consult a doctor when sleeplessness continues for more than two weeks is a signal to reassess the problem. It is not a guarantee that two weeks of nightly use is appropriate for everyone.[1]
How much does it improve sleep
A 2005 randomized, placebo-controlled trial enrolled 184 adults with mild insomnia; 60 received diphenhydramine for two weeks. Participants reported modest improvements, including better sleep efficiency, but few comparisons with placebo were statistically significant. Laboratory sleep recordings did not show significant differences between groups in sleep continuity. No serious adverse events were reported, but this short study could not establish safety over months or years.[2]
The American Academy of Sleep Medicine’s 2017 guideline suggests against diphenhydramine for difficulty falling asleep or staying asleep in adults with chronic insomnia. Its analysis found that improvements did not reach the guideline’s thresholds for clinical importance. The recommendation is rated weak because the evidence is limited and uncertain, not because nightly use has been proved harmless or because no individual could benefit. Short trials in selected participants cannot establish reliable long-term effectiveness.[3]
More recent guidance is consistent: the 2025 VA/DoD guideline also suggests against diphenhydramine when medication is offered for chronic insomnia, again with a weak recommendation against its use.[13]
Why the sleepy effect may fade
Tolerance means a response becomes smaller with repeated exposure. In a 2002 randomized crossover trial, 15 healthy men aged 18 to 50 received diphenhydramine or placebo twice daily for four days. Diphenhydramine caused greater sleepiness initially, but by day four the sleepiness measurements were indistinguishable from placebo.[4]
This was a daytime-sedation experiment, not a trial of long-term bedtime treatment in people with insomnia. It therefore cannot tell us exactly when, or whether, any particular nightly user will notice reduced benefit. It does demonstrate that the sedating effect can diminish quickly. Reduced sleepiness also does not establish that every other medication risk has disappeared.[4,5]
Effects can carry into the next day
A randomized crossover study published in 2012 tested bedtime antihistamines in 22 healthy men. Diphenhydramine was associated with next-day sleepiness and poorer psychomotor performance, meaning performance on tasks requiring attention and coordinated responses. The small, all-male sample limits how precisely the findings apply to other populations.[7]
A 2016 crossover trial in 59 healthy volunteers also found impairment on one simulated-driving measure after nighttime diphenhydramine. Not every comparison showed a significant effect, and the study allowed only 6.5 hours before participants were awakened for evaluation. These findings support a possibility of residual impairment, not a prediction that everyone will be impaired after every dose. FDA also cautions that antihistamines can affect driving even when a person does not feel noticeably drowsy.[8,9]
Why age and other medicines matter
Diphenhydramine has strong anticholinergic effects. These can cause dry mouth, constipation and confusion. The American Geriatrics Society’s 2023 Beers Criteria recommends avoiding oral diphenhydramine in most adults aged 65 and older, citing these effects, reduced clearance with age and tolerance when used as a sleep medicine. The criteria recognize exceptions for some other indications, such as acute severe allergic reactions; they are not a blanket prohibition in every clinical situation.[5]
The total anticholinergic burden matters as well. Taking several medicines with these properties can increase the risk of cognitive problems, delirium and falls or fractures. Assessing one sleep aid in isolation can miss that combined burden.[5]
What the dementia studies do and do not show
Long-term concerns deserve careful wording. A 2015 prospective study followed 3,434 adults aged 65 and older who did not have dementia at enrollment. Greater cumulative exposure to strong anticholinergic medicines was associated with a higher rate of dementia. The exposure included several medication classes, not diphenhydramine alone.[10]
Results are not uniform across drug classes. A 2019 study comparing 58,769 people with dementia with 225,574 matched controls found associations for several anticholinergic medication groups, but no statistically significant increase for antihistamines.[11]
Both studies were observational. They cannot prove that diphenhydramine causes dementia, separate every medication effect from the conditions being treated, or provide an individual risk estimate for occasional Benadryl use. Equally, the absence of a significant antihistamine association in one study is not proof of long-term safety. The balanced interpretation is concern about unnecessary cumulative anticholinergic exposure, without presenting dementia as an established consequence of this particular medicine.[10,11]
A better approach to recurring insomnia
For recurring sleep problems, a clinician can review possible causes and the complete medication list, including “PM,” cold and allergy products. The label warns against alcohol and duplicate diphenhydramine, and calls for professional advice with sedatives, glaucoma, certain breathing problems or difficulty urinating; pregnancy and breastfeeding also require a check. Follow its two-week sleeplessness warning rather than repeatedly extending self-treatment.[1] For chronic insomnia, cognitive behavioral therapy for insomnia, or CBT-I, is the recommended first-line approach. It addresses sleep-related behaviors and thoughts, has a strong AASM recommendation, and is more than general sleep-hygiene advice.[3,12] The research favors a treatment plan for persistent insomnia over routine nightly diphenhydramine.
References
- DailyMed. Nighttime Sleep Aid (diphenhydramine hydrochloride), Prodose, Inc. OTC Drug Facts label updated January 26, 2026. Indication, duplicate-ingredient warning, alcohol and sedative precautions, medical-condition precautions, and two-week warning.
- Morin CM, Koetter U, Bastien C, Ware JC, Wooten V. Valerian-hops combination and diphenhydramine for treating insomnia: a randomized placebo-controlled clinical trial. Sleep. 2005;28(11):1465–1471. doi:10.1093/sleep/28.11.1465.
- Sateia MJ et al. AASM pharmacologic treatment guideline for chronic insomnia in adults. J Clin Sleep Med. 2017;13(2):307–349. doi:10.5664/jcsm.6470. Recommendation 11 and introductory guidance on CBT-I.
- Richardson GS, Roehrs TA, Rosenthal L, Koshorek G, Roth T. Tolerance to daytime sedative effects of H1 antihistamines. J Clin Psychopharmacol. 2002;22(5):511–515. doi:10.1097/00004714-200210000-00012.
- American Geriatrics Society Beers Criteria Update Expert Panel. 2023 updated AGS Beers Criteria for potentially inappropriate medication use in older adults. J Am Geriatr Soc. 2023;71(7):2052–2081. doi:10.1111/jgs.18372. Tables 2 and 5; adults aged 65 and older.Verified table copy hosted by University of Connecticut: https://health.uconn.edu/pharmacy/wp-content/uploads/sites/60/2023/11/2023-American-Geriatrics-Society-Beers-Criteria-1.pdf
- DailyMed. Benadryl Allergy Liqui-Gels (diphenhydramine hydrochloride), Kenvue Brands LLC. OTC Drug Facts label updated May 7, 2026.
- Katayose Y et al. Carryover effect on next-day sleepiness and psychomotor performance of nighttime administered antihistaminic drugs: a randomized controlled trial. Hum Psychopharmacol. 2012;27(4):428–436. doi:10.1002/hup.2244.
- Kay GG et al. Next-day residual effects of gabapentin, diphenhydramine, and triazolam on simulated driving performance in healthy volunteers [randomized crossover trial]. Hum Psychopharmacol. 2016;31(3):217–226. doi:10.1002/hup.2530.
- U.S. Food and Drug Administration. Some Medicines and Driving Don’t Mix. Official consumer safety guidance, accessed October 31, 2026.
- Gray SL 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.
- Coupland CAC, Hill T, Dening T, Morriss R, Moore M, Hippisley-Cox J. Anticholinergic drug exposure and the risk of dementia: a nested case-control study. JAMA Intern Med. 2019;179(8):1084–1093. doi:10.1001/jamainternmed.2019.0677.
- Edinger JD et al. AASM behavioral and psychological treatment guideline for chronic insomnia in adults. J Clin Sleep Med. 2021;17(2):255–262. doi:10.5664/jcsm.8986. Strong recommendation for multicomponent CBT-I; recommendation against sleep hygiene alone.
- U.S. Department of Veterans Affairs and Department of Defense. Clinical Practice Guideline for the Management of Chronic Insomnia Disorder and Obstructive Sleep Apnea. 2025. Recommendation 10; weak against diphenhydramine when pharmacotherapy is offered for chronic insomnia. Official September 15, 2025 PDF version.