If you've struggled with insomnia, you may have tried Benadryl, Unisom or another over-the-counter nighttime sleep aid.
These medications can make people sleepy. They're inexpensive, widely available and often perceived as harmless because they don't require a prescription.
But some have an important property that isn't always obvious from the packaging: strong anticholinergic activity.
Researchers have linked greater cumulative exposure to certain anticholinergic medications with increased rates of dementia. At the same time, the research does not prove that taking Benadryl or Unisom causes Alzheimer's disease.
1. What's Actually in Benadryl and Unisom?
Before discussing risk, it's important to identify the actual medication. Brand names can be misleading.
| Product | Active ingredient | Medication class |
|---|---|---|
| Benadryl Allergy (common U.S. oral formulation) | Diphenhydramine | First-generation antihistamine |
| Unisom SleepTabs | Doxylamine succinate | First-generation antihistamine |
| Unisom SleepGels | Diphenhydramine hydrochloride | First-generation antihistamine |
| Some nighttime cold and allergy products | May contain diphenhydramine or doxylamine | Depends on formulation |
Both diphenhydramine and doxylamine are classified as first-generation antihistamines with strong anticholinergic properties.
However, not every antihistamine has the same effects. Newer allergy medications generally differ in their ability to enter the brain and produce anticholinergic side effects.
Also, not every product sold under a familiar brand contains the same ingredient. Always read the current Drug Facts label.
2. How Do These Medications Make You Sleepy?
Histamine is a chemical messenger that helps maintain wakefulness in the brain.
First-generation antihistamines cross the blood-brain barrier and block histamine H1 receptors. This can produce drowsiness.
But diphenhydramine and doxylamine also block muscarinic acetylcholine receptors.
That second action is responsible for many of their anticholinergic effects.
What is acetylcholine?
Acetylcholine is a neurotransmitter involved in many functions, including:
- Attention and concentration.
- Learning and memory.
- Muscle activation.
- Saliva production.
- Intestinal movement.
- Bladder function.
- Eye focusing.
- Body-temperature regulation.
When a medication blocks some of these pathways, its effects can extend well beyond sleepiness.
3. Short-Term Anticholinergic Side Effects
Unlike the long-term dementia question, many short-term anticholinergic effects are well recognized.
Memory and thinking
Strong anticholinergic medications may temporarily impair attention, working memory, concentration and mental clarity.
Some people describe a foggy or unusually slow feeling the next day.
Balance and coordination
Sedation and impaired reaction time can increase the risk of falls, particularly when getting out of bed at night.
Dry mouth and constipation
Blocking acetylcholine can reduce saliva production and slow intestinal movement.
Urinary retention
Some people may experience difficulty starting urination or emptying the bladder. This can be especially concerning with an enlarged prostate or other urinary problems.
Blurred vision and overheating
Anticholinergic activity can affect eye focusing and reduce sweating. In some situations, this can increase the risk of overheating.
Confusion and delirium
In vulnerable individuals, especially older adults, these medicines can contribute to acute confusion or delirium.
Delirium is a sudden change in attention, awareness or thinking. It is different from dementia, which typically develops over a longer period.
4. What Does the Research Say About Dementia?
Several large observational studies have examined whether people with greater cumulative exposure to anticholinergic medications are more likely to receive a dementia diagnosis.
These studies have raised legitimate concerns. However, they have not all produced identical results, especially when researchers examine individual drug classes.
Study 1: Gray and Colleagues, 2015
Published in JAMA Internal Medicine, this prospective cohort study followed 3,434 adults aged 65 and older who did not have dementia at enrollment.
Researchers examined cumulative exposure to strong anticholinergic medications using pharmacy dispensing records over time.
During an average follow-up of 7.3 years, 797 participants developed dementia.
The study found a dose-response pattern: greater cumulative exposure was associated with greater dementia risk.
Importantly, the exposure included several medication classes, including antidepressants, first-generation antihistamines and bladder medications.
The results do not provide a specific dementia-risk estimate for an individual occasionally taking Benadryl or Unisom.
Study 2: Richardson and Colleagues, 2018
A large case-control study published in The BMJ examined 40,770 people with dementia and 283,933 controls.
The researchers studied prescription records from years before dementia diagnosis.
They found associations involving certain anticholinergic antidepressants, bladder medications and Parkinson's disease medications.
However, they did not find a statistically significant association for the antihistamine category overall in their main class-specific analysis.
This is an important counterpoint to claims that every anticholinergic drug has been shown to carry the same dementia risk.
The study also had limitations, including incomplete capture of over-the-counter antihistamine use.
Study 3: Coupland and Colleagues, 2019
Another large study in JAMA Internal Medicine examined 58,769 people diagnosed with dementia and 225,574 controls.
Researchers found that greater cumulative anticholinergic exposure was associated with increased dementia risk.
The strongest class-specific associations involved certain antidepressants, bladder medications, antipsychotics, antiepileptic medications and Parkinson's disease medications.
Again, the study did not identify a statistically significant increased dementia risk for antihistamines as a separate class.
That does not prove antihistamines are harmless, particularly because over-the-counter use can be difficult to measure.
More Recent Evidence: 2025 Umbrella Review
A 2025 umbrella review examined systematic reviews of medications and dementia risk.
For anticholinergic medications, pooled relative-risk estimates from three meta-analyses ranged from approximately 1.20 to 1.46.
The review found evidence suggesting a relationship between greater exposure and higher dementia risk.
However, there was substantial variation among studies and insufficient detail about specific anticholinergic medication classes.
This means the pooled estimates should not be presented as Benadryl-specific or Unisom-specific risks.
What do these studies mean together?
They support concern about substantial cumulative exposure to strong anticholinergic medications.
But they also show why careful interpretation matters: associations differ by medication class, and the strongest evidence is not necessarily specific to OTC nighttime antihistamines.
5. What the Research Cannot Prove
It would be misleading to claim that Benadryl or Unisom has been conclusively shown to cause Alzheimer's disease.
Most of the influential long-term studies are observational.
They compare medication exposure and later health outcomes, but cannot fully eliminate alternative explanations.
Confounding by indication
The conditions being treated may themselves be associated with dementia risk.
For example, depression, sleep problems and certain neurological symptoms may occur before dementia is diagnosed.
Reverse causation
Some people may receive medications for early symptoms of an illness that has not yet been recognized.
Researchers try to address this by excluding medication exposure close to the dementia diagnosis, but uncertainty remains.
Incomplete OTC records
Pharmacy prescription databases may not capture every purchase of Benadryl or Unisom.
That makes it difficult to calculate exposure to these products precisely.
Different drugs, different effects
Anticholinergic medications vary in how strongly they block receptors, how readily they enter the brain, and how the body processes them.
It is therefore inappropriate to assume that every anticholinergic medication carries an identical long-term risk.
6. What Is Anticholinergic Burden?
Anticholinergic burden refers to the combined effects of medications with anticholinergic properties.
Someone might use a nighttime antihistamine, a bladder medication and an antidepressant without realizing all three may contribute to anticholinergic exposure.
Examples of medications worth reviewing
| Category | Examples | Why it matters |
|---|---|---|
| First-generation antihistamines | Diphenhydramine, doxylamine, hydroxyzine | Strong anticholinergic activity and sedation. |
| Some antidepressants | Amitriptyline, nortriptyline, paroxetine | Can contribute substantially to anticholinergic burden. |
| Some bladder medications | Oxybutynin, tolterodine | May contribute to cognitive and other anticholinergic effects. |
| Some motion-sickness medicines | Scopolamine, meclizine | May cause sedation or anticholinergic side effects. |
| Some muscle relaxants | Cyclobenzaprine | Can add sedation and anticholinergic effects. |
Examples are not exhaustive. Risk varies by drug, dose, duration and individual. Medication-burden scales are screening tools, not exact predictors of dementia.
The American Geriatrics Society recommends considering total anticholinergic burden during medication reviews.
7. Why Are Older Adults at Greater Risk?
Aging can change the way medications are absorbed, distributed and cleared from the body.
Older adults may also be more vulnerable to medication-related confusion, sedation and falls.
The American Geriatrics Society recommendation
The 2023 AGS Beers Criteria recommend avoiding first-generation antihistamines, including oral diphenhydramine and doxylamine, in most older adults.
Reasons include:
- Strong anticholinergic activity.
- Confusion and cognitive impairment.
- Constipation and dry mouth.
- Reduced drug clearance with advanced age.
- Development of tolerance when used as sleeping medicines.
- Concerns involving falls, delirium and cumulative exposure.
These criteria are prescribing guidance rather than an absolute prohibition in every circumstance.
For example, diphenhydramine may have a role in certain acute allergic reactions under appropriate medical guidance.
8. What Are Safer Approaches to Chronic Insomnia?
If someone has relied on nighttime antihistamines for months or years, the next question is often: What else can help?
CBT-I: The strongest starting point
Cognitive behavioral therapy for insomnia, known as CBT-I, is recommended as a first-line treatment for chronic insomnia in adults.
It addresses behavioral and psychological patterns that can perpetuate sleep difficulties.
CBT-I typically includes:
- Stimulus control.
- Individualized sleep scheduling.
- Cognitive strategies for unhelpful sleep-related beliefs.
- Education about sleep and circadian rhythms.
- Strategies for managing wakefulness without reinforcing insomnia.
CBT-I is more than a list of generic sleep hygiene tips.
Look for treatable causes
Persistent sleep problems may involve:
- Obstructive sleep apnea.
- Restless legs syndrome.
- Chronic pain.
- Medication side effects.
- Circadian rhythm disorders.
- Depression or anxiety.
- Other medical or neurological conditions.
Identifying the underlying problem may be more useful than repeatedly trying new sedating products.
What about prescription sleep medicines?
Prescription options have different mechanisms, benefits and risks.
Some are not strongly anticholinergic, but that does not automatically make them risk-free.
A clinician can consider the type of insomnia, age, medical conditions and medication interactions when discussing treatment choices.
Avoid replacing one sleep aid with another without reviewing the overall risk-benefit picture.
9. What If You've Taken Benadryl or Unisom for Years?
Learning about anticholinergic risks can be unsettling, especially for someone who has used these medicines regularly.
But past use does not mean dementia is inevitable.
There is no reliable formula that can calculate your personal dementia risk from a history of OTC sleep medication use.
A Practical Medication-Review Checklist
- Identify the ingredient. Check whether your product contains diphenhydramine, doxylamine or something else.
- Estimate how often you use it. Occasional use and nightly use over years are different exposure patterns.
- Make a complete medication list. Include prescriptions, allergy medicines, cold products, supplements and nighttime aids.
- Ask about anticholinergic burden. A pharmacist can help identify overlapping effects.
- Discuss alternatives. Ask whether CBT-I, evaluation of sleep disorders or another treatment would better address the underlying problem.
- Plan changes safely. If you use a medication regularly, discuss an appropriate transition with a clinician.
Questions worth asking your pharmacist or doctor
- Does this medicine have strong anticholinergic effects?
- Do any of my other medicines add to that burden?
- Could it be contributing to daytime fatigue, dizziness or memory problems?
- Are there alternatives with fewer anticholinergic effects?
- Could my insomnia have an untreated medical cause?
- What is the safest way to change my current routine?
10. Frequently Asked Questions
Does Benadryl cause Alzheimer's disease?
Research has linked greater cumulative anticholinergic exposure with dementia in some observational studies. However, a direct causal relationship between Benadryl use and Alzheimer's disease has not been established. Some large studies did not find statistically significant dementia associations for antihistamines analyzed separately.
Is Unisom safer than Benadryl?
That depends on the formulation and the individual. Unisom SleepTabs contain doxylamine; SleepGels contain diphenhydramine. Both are first-generation antihistamines with strong anticholinergic properties. Neither is generally recommended for routine long-term insomnia treatment, particularly in older adults.
What if I only use one occasionally?
Occasional use is different from years of regular exposure. The major dementia studies cannot establish an individual risk from an occasional dose. Short-term effects such as sedation, impaired coordination and confusion can still occur.
Can these medications cause memory problems the next day?
Yes. Strong anticholinergic medicines may impair attention and memory, particularly in susceptible individuals. Sedation may also persist into the next morning.
Are all antihistamines anticholinergic?
No. Antihistamines differ in their pharmacological effects. First-generation agents such as diphenhydramine and doxylamine have strong anticholinergic activity. Many newer allergy medicines have less central anticholinergic activity.
Does stopping an anticholinergic medicine reverse dementia risk?
Research has not established that stopping a medication reverses a long-term dementia association. However, reducing unnecessary anticholinergic exposure may improve certain medication-related side effects and is an appropriate topic for clinical review.
Can anticholinergic medicines affect people younger than 65?
Yes. Dry mouth, constipation, sedation and impaired attention can occur at younger ages. Long-term dementia research has focused heavily on middle-aged and older adults, so the risks for younger populations are less clearly defined.
Should I worry if I've used Benadryl for many years?
A history of use is a reason to review your medications, not a reason to assume dementia will develop. A clinician can help assess current risks, possible side effects and safer options.
11. Research and References
The following sources include primary research, systematic reviews and professional clinical guidance.
- Gray SL, et al. (2015). Cumulative Use of Strong Anticholinergics and Incident Dementia: A Prospective Cohort Study. JAMA Internal Medicine. Full study .
- Richardson K, et al. (2018). Anticholinergic Drugs and Risk of Dementia: Case-Control Study. The BMJ. Full study .
- Coupland CAC, et al. (2019). Anticholinergic Drug Exposure and the Risk of Dementia: A Nested Case-Control Study. JAMA Internal Medicine. Full study .
- Systemic Medications and Dementia Risk (2025). Systematic umbrella review. Molecular Psychiatry. Full review .
- American Geriatrics Society (2023). Updated AGS Beers Criteria for Potentially Inappropriate Medication Use in Older Adults. Full guideline .
- American College of Physicians (2016). Management of Chronic Insomnia Disorder in Adults: Clinical Practice Guideline. Guideline summary .
These studies examine different populations, medication categories and exposure periods. Their estimates should not be treated as individualized risk predictions or proof of causation.
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