Long-term use of Benadryl (diphenhydramine) is associated with a significantly higher risk of dementia. A large study published in JAMA Internal Medicine found that people who took anticholinergic drugs like Benadryl for three years or more had a 54% higher risk of dementia compared to those who took the same dose for three months or less. The risk increased with cumulative dose, meaning the more you take over time, the greater the concern.
What the Research Shows
The strongest evidence comes from a prospective study that tracked older adults over time and measured their cumulative use of anticholinergic medications, the drug class Benadryl belongs to. The relationship between dose and dementia risk followed a clear pattern: higher lifetime use meant higher risk. Three years of regular use marked the threshold where risk jumped most sharply, but the association was dose-dependent, meaning even moderate long-term use showed some elevation in risk.
This wasn’t an isolated finding. A meta-analysis in the journal Age and Ageing confirmed the broader pattern, linking anticholinergic drug use to increased rates of dementia, mild cognitive impairment, and cognitive decline across multiple studies. The consistency of results across different research groups and populations is what makes this finding particularly concerning.
One important caveat: these are observational studies. They can show a strong association but can’t definitively prove that Benadryl causes dementia. It’s possible, for instance, that people who use these drugs frequently already have early, undetected changes in their brains. Still, the biological plausibility (discussed below) and the dose-response relationship make the link hard to dismiss.
How Benadryl Affects the Brain
Benadryl works by blocking a chemical messenger called acetylcholine. That’s what makes you drowsy and dries up a runny nose. But acetylcholine also plays a critical role in memory and learning, and the brain regions most dependent on it, particularly those involved in forming new memories, are the same regions that deteriorate in Alzheimer’s disease.
Brain imaging studies of cognitively normal older adults taking anticholinergic medications have shown reduced brain metabolism and greater brain shrinkage in memory-related areas. Blocking acetylcholine over long periods appears to trigger a cascade of harmful effects: it can promote the death of brain cells, increase levels of the protein plaques and tangles associated with Alzheimer’s, and dysregulate the body’s stress hormone system in ways that further damage vulnerable brain tissue. In short, the drug doesn’t just temporarily impair cognition. Chronic use may accelerate the kind of brain changes seen in dementia.
Occasional Use vs. Long-Term Use
If you’ve taken Benadryl a handful of times for a bad allergic reaction or a rough night of sleep, the research should not alarm you. The 54% increased risk was tied to the equivalent of daily use for three or more years. Short-term, occasional use at low cumulative doses was not associated with the same level of risk.
The concern is really about the pattern many people fall into without realizing it: taking Benadryl nightly as a sleep aid, or using combination products like Tylenol PM or Advil PM (which contain diphenhydramine) on a regular basis for months or years. That kind of steady, cumulative exposure is what drives up risk. It’s also worth knowing that the foggy, sluggish feeling many people get from Benadryl the morning after taking it is a real-time sign of its anticholinergic effect on the brain.
Where Benadryl Ranks Among Anticholinergics
Not all antihistamines carry the same risk. The Anticholinergic Cognitive Burden (ACB) scale, developed by researchers at Indiana University, scores medications from 1 to 3 based on how strongly they block acetylcholine. Benadryl scores a 3, the highest category, meaning it is a “definite anticholinergic” with evidence it can cause delirium and cognitive impairment.
Other common over-the-counter drugs that also score a 3 include:
- Doxylamine (Unisom), another popular OTC sleep aid
- Dimenhydrinate (Dramamine), used for motion sickness
- Meclizine (Antivert), used for vertigo and nausea
By comparison, newer antihistamines like cetirizine (Zyrtec) and loratadine (Claritin) score only a 1, placing them in the “possible” anticholinergic category with far less concern for brain effects.
Can the Damage Be Reversed?
This is the question most people want answered, and unfortunately the evidence is not encouraging. Clinical trials that stopped anticholinergic medications and then measured cognitive function afterward did not find clear improvements. Those trials were small and only tracked participants for short periods, so they aren’t the final word. But as of now, there’s no solid evidence that stopping the drug reverses cognitive changes that have already occurred. That makes prevention, specifically avoiding long-term use in the first place, the more reliable strategy.
Safer Alternatives for Allergies
The 2023 American Geriatrics Society Beers Criteria, the most widely used guide for medication safety in older adults, specifically flags diphenhydramine as a drug to avoid. It recommends several alternatives for allergy symptoms:
- Steroid nasal sprays like fluticasone (Flonase), which target nasal inflammation directly without anticholinergic effects
- Newer antihistamines like cetirizine (Zyrtec), fexofenadine (Allegra), or loratadine (Claritin), which don’t cross into the brain as readily
- Saline nasal rinses for mild congestion, using only sterilized water
Safer Alternatives for Sleep
Many people reach for Benadryl not because of allergies but because it makes them sleepy. This is one of the most common ways people accumulate a high lifetime dose without thinking of it as a medication habit. The PM versions of common pain relievers (Tylenol PM, Advil PM) are essentially just the pain reliever plus Benadryl, and they’re marketed in a way that makes nightly use seem harmless.
For older adults especially, several sleep medications carry less cognitive risk. Melatonin and ramelteon work by supporting the body’s natural sleep-wake cycle rather than sedating through antihistamine pathways. A newer class of sleep drugs called orexin receptor antagonists (suvorexant, lemborexant, daridorexant) block wakefulness signals in the brain and have been studied specifically in adults over 55. Low-dose doxepin, at doses far below its antidepressant range, is the only antidepressant with FDA approval for insomnia and works differently from traditional anticholinergics. All of these are prescription options worth discussing if you’ve been relying on Benadryl or similar products for sleep.
Non-drug approaches also have strong evidence for insomnia, particularly cognitive behavioral therapy for insomnia (CBT-I), which addresses the thought patterns and habits that keep people awake. For many people it’s more effective than medication over the long term, with none of the chemical burden.