Is It Safe to Take Benadryl for Sleep?

What does Benadryl actually do for sleep?

Diphenhydramine — the active ingredient in Benadryl, ZzzQuil, Unisom SleepTabs, and most over-the-counter sleep aids — is a first-generation antihistamine. Its sedation is a side effect of its mechanism, not a purpose-built sleep action. It works by broadly blocking histamine and other brain receptors, producing drowsiness — but it does not replicate normal sleep architecture the way restorative natural sleep or some prescription medications do.

Systematic reviews of over-the-counter sleep aids have found that diphenhydramine lacks robust, consistent clinical evidence for improving either subjective sleep quality or objective polysomnography measures 1Ref 1Culpepper L, Wingertzahn MA (2015).Over-the-Counter Agents for the Treatment of Occasional Disturbed Sleep or Transient Insomnia: A Systematic Review of Efficacy and Safety.Diphenhydramine lacks robust, consistent clinical evidence for improving subjective or polysomnographic sleep measures. That does not mean it never helps — many people find it useful on an occasional tough night — but the evidence base for routine use is weak.

How quickly does tolerance develop?

The body adapts to diphenhydramine's sedating effect quickly. An expert consensus published in 2025 in the Journal of Clinical Medicine noted that tolerance to the sedative effects can emerge within three to four days of uninterrupted use 2Ref 2Ariza-Salamanca DF, Venegas M, Parejo K, Amado S, Echeverry J, Calderón-Ospina CA (2025).Expert Consensus on the Use of Diphenhydramine for Short-Term Insomnia: Efficacy, Safety, and Clinical Applications.Tolerance to sedative effects develops within 3-4 days of continuous use; diphenhydramine prolongs REM latency and reduces REM sleep percentage; experts recommend only short-term use. A separate systematic review found that by day three of continuous use in one study, the alertness-reducing effect had largely disappeared.

The practical result: people who start using diphenhydramine every night often find it stops working within the first week. Rather than stopping, many continue nightly use despite diminishing returns — not because diphenhydramine is physically addictive in the classic sense, but because the underlying sleep problem was never treated and now there is no medication bridge either. That pattern can be difficult to step back from.

What are the side effects worth knowing about?

Diphenhydramine's broad receptor blockade causes more than drowsiness. Common effects include:

• Next-day grogginess — residual sedation can impair driving, reaction time, and work performance the morning after
• Dry mouth, constipation, blurred vision — from its anticholinergic (acetylcholine-blocking) action
• Difficulty urinating — anticholinergic effects can worsen urinary flow, which matters most for men with an enlarged prostate (BPH)
• Reduced REM sleep — research shows diphenhydramine prolongs REM latency and reduces the proportion of REM sleep, which may affect how restorative sleep feels 2Ref 2Ariza-Salamanca DF, Venegas M, Parejo K, Amado S, Echeverry J, Calderón-Ospina CA (2025).Expert Consensus on the Use of Diphenhydramine for Short-Term Insomnia: Efficacy, Safety, and Clinical Applications.Tolerance to sedative effects develops within 3-4 days of continuous use; diphenhydramine prolongs REM latency and reduces REM sleep percentage; experts recommend only short-term use

For most healthy adults using it occasionally, these effects are mild and temporary. They become more significant at higher doses, with regular use, or in certain groups (see below).

Why are older adults specifically advised against it?

Diphenhydramine is included on the American Geriatrics Society Beers Criteria — a regularly updated evidence-based list of medications that are potentially inappropriate for adults 65 and older 3Ref 32023 American Geriatrics Society Beers Criteria Update Expert Panel (2023).American Geriatrics Society 2023 updated AGS Beers Criteria for potentially inappropriate medication use in older adults.Diphenhydramine (first-generation antihistamine) is on the Beers Criteria list of potentially inappropriate medications for adults 65 and older due to anticholinergic effects, fall risk, and confusion. The reasons are specific to how older bodies handle the drug:

• Slower clearance: older adults metabolize the drug more slowly, meaning the sedating and anticholinergic effects last longer and are more intense
• Fall risk: excessive sedation combined with impaired coordination increases the risk of nighttime falls, a major cause of injury in older adults
• Confusion: anticholinergic effects can cause or worsen confusion, especially in people who already have mild cognitive changes
• Possible link to dementia with long-term use: a large nested case-control study (nearly 59,000 dementia cases) found that cumulative exposure to anticholinergic drugs was associated with increased dementia risk, with adjusted odds ratios rising up to 1.49 at the highest exposure levels over 10 years 4Ref 4Coupland CAC, Hill T, Dening T, Morriss R, Moore M, Hippisley-Cox J (2019).Anticholinergic Drug Exposure and the Risk of Dementia: A Nested Case-Control Study.Cumulative anticholinergic drug exposure associated with increased dementia risk (AOR up to 1.49 at highest exposure over 10 years) in a nested case-control study of ~59,000 dementia cases. Whether this association is causal remains debated, but it adds weight to the geriatric recommendation to avoid this drug class when alternatives exist.

For older adults struggling with sleep, this is an area worth a direct conversation with a clinician rather than relying on an OTC option.

Who else should be cautious?

Beyond older adults, a few groups warrant particular attention:

Enlarged prostate (BPH): Diphenhydramine's anticholinergic effect can cause or worsen urinary retention — a painful inability to urinate. Men with prostate enlargement should check with a clinician before using it.

Closed-angle glaucoma: Anticholinergic medications can raise intraocular pressure. Anyone with this form of glaucoma should avoid diphenhydramine without explicit guidance from a clinician.

Pregnancy and breastfeeding: OTC sleep aids should not be taken during pregnancy or breastfeeding without explicit guidance from an obstetrician or midwife. The drug passes into breast milk and has been associated with irritability and sleep-pattern changes in breastfed infants at higher or frequent doses.

Alcohol and other sedating medications: Combining diphenhydramine with alcohol intensifies sedation unpredictably. Many anxiety medications, muscle relaxants, opioids, and older antidepressants have additive sedating and anticholinergic effects — a review with a pharmacist or clinician is worthwhile if you are on other medications.

What actually works better for ongoing sleep problems?

If you are reaching for a sleep aid most nights, the most evidence-supported first-line treatment is Cognitive Behavioral Therapy for Insomnia (CBT-I) — not medication. An American Academy of Sleep Medicine clinical practice guideline positions CBT-I as the recommended behavioral treatment for chronic insomnia in adults 5Ref 5Edinger JD, Arnedt JT, Bertisch SM, et al. (2021).Behavioral and Psychological Treatments for Chronic Insomnia Disorder in Adults: An American Academy of Sleep Medicine Clinical Practice Guideline.AASM guideline recommends CBT-I as the evidence-supported behavioral treatment for chronic insomnia in adults. A systematic review and meta-analysis across 37 randomized controlled trials found that CBT-I produced clinically meaningful and durable improvements in sleep onset, wake time, and sleep efficiency, with effects maintained at follow-up 6Ref 6Trauer JM, Qian MY, Doyle JS, Rajaratnam SMW, Cunnington D (2015).Cognitive Behavioral Therapy for Chronic Insomnia: A Systematic Review and Meta-analysis.CBT-I produces clinically meaningful and durable improvements in sleep onset, wake time, and sleep efficiency across 37 randomized controlled trials.

What makes CBT-I different from medication is that it targets the thoughts and behaviors that sustain insomnia — irregular schedules, time-in-bed mismatches, worry about sleep itself — rather than temporarily sedating the problem away. Results build over weeks rather than one night, but they last.

CBT-I is available through therapists trained in sleep, some primary care clinicians, telehealth platforms, and digital CBT-I programs. When medication is appropriate, a clinician can discuss options that are better studied and more targeted than diphenhydramine.