Every spring and fall, millions of people across the country reach for allergy medicine to stop the sneezing, itchy eyes, and runny noses that come with pollen, dust, or mold. For many, cetirizine, known by its brand name Zyrtec, is the product they grab from the medicine cabinet. It’s quick, easy, and available over the counter.

But as public awareness of brain health grows, more people are asking questions about the long-term effects of everyday medications. Could something as common as an allergy pill affect your brain, or even increase your risk of Alzheimer’s disease or other types of dementia?

This concern began with older medications such as diphenhydramine (Benadryl), which doctors have long known can make people feel groggy or confused. Researchers eventually discovered that some of these older drugs also interfere with brain chemicals that help with memory and thinking. But not all medicines act the same way, and understanding those differences can help you protect both your comfort and your cognition.

What Is Zyrtec?

Cetirizine (Zyrtec) is an antihistamine. When you have an allergic reaction to pollen, pet dander, or even dust, your body releases a chemical called histamine. Histamine causes itching, swelling, and other allergy symptoms. Cetirizine blocks histamine from attaching to its receptors, helping stop those symptoms before they start.

Cetirizine is considered a second-generation antihistamine. These drugs were developed to relieve allergy symptoms while avoiding the heavy drowsiness that often comes with first-generation antihistamines, such as diphenhydramine or chlorpheniramine (Chlor-Trimeton).

The key difference lies in how easily these drugs enter the brain.

How Antihistamines Affect the Brain

Histamine isn’t just an allergy chemical — it’s also a neurotransmitter, a messenger that helps your brain regulate alertness, focus, and memory.

Older, first-generation antihistamines can cross the blood-brain barrier, a layer of cells that protects the brain from many substances in the bloodstream. Once inside, they don’t just block histamine, they also block another important neurotransmitter called acetylcholine.

Acetylcholine plays a vital role in memory and learning. When it’s blocked, people can experience side effects such as drowsiness, slower reaction times, and difficulty concentrating. When this blockage happens often or over long periods, it can contribute to cognitive decline.

Drugs that interfere with acetylcholine are described as anticholinergic. This group includes some antihistamines as well as certain bladder medications, antidepressants, and sleep aids.

One large, well-known study published in 2015 followed more than 3,000 adults aged 65 and over. The researchers found that people who used strong anticholinergic drugs daily for three years or more were significantly more likely to develop dementia — including Alzheimer’s disease — than those who used them for less time.

Zyrtec vs. Benadryl: Key Differences

Many people assume that all allergy medications are similar because they relieve the same symptoms. But when it comes to how they affect the brain, the differences are important.

Diphenhydramine is a first-generation antihistamine that crosses into the brain easily. It’s well known for causing sleepiness and sometimes confusion. Its strong anticholinergic effects make it more likely to interfere with memory and attention.

Cetirizine, on the other hand, is a second-generation antihistamine that rarely causes sleepiness and confusion. It stays mostly outside the brain and does not significantly block acetylcholine.

This difference explains why cetirizine is often labeled as a “nondrowsy” or “low-drowsiness” medicine, while diphenhydramine is not. It also explains why long-term use of diphenhydramine has been linked with dementia risk in older adults, while cetirizine has not.

Does Zyrtec Increase Alzheimer’s Risk?

Fortunately, cetirizine is not a strong anticholinergic medication.

Because of how it’s designed, cetirizine has a very limited ability to cross into the brain. Most of its activity stays in the body’s tissues — like the nose, eyes, and skin — where histamine causes allergy symptoms. That means it’s much less likely to interfere with brain function or memory.

Newer (second-generation) antihistamines such as cetirizine, loratadine (Claritin), and fexofenadine (Allegra) have little to no evidence linking them to dementia. They are considered to be much safer for the brain than the older allergy medicines.

In contrast, older antihistamines like diphenhydramine can enter the brain easily and block acetylcholine strongly. When used often over long periods, such as for sleep or chronic allergies, these drugs can contribute to cognitive problems in older adults.

So while cetirizine isn’t entirely without side effects (some people still experience mild sleepiness or fatigue), there’s no evidence that it increases Alzheimer’s risk.

What the Research Says

Newer research helps clarify how antihistamines and other anticholinergic drugs may relate to dementia risk. Large, long-term studies show that people who take many anticholinergic medications, such as certain antidepressants, bladder drugs, and antipsychotics, have a greater risk of developing dementia later in life.

However, these same studies found no clear link between antihistamines overall and dementia. In fact, when researchers looked specifically at allergy medications, they found no increase in dementia risk among users of first- or second-generation antihistamines.

In older adults, there was a small increase in dementia risk among frequent antihistamine users, but researchers noted this was likely due to age and health factors, not the medications themselves.

A 2024 review of multiple studies confirmed that anticholinergic drugs as a group can affect brain health when taken in high amounts or over many years, but second-generation antihistamines like cetirizine were not among the drugs that raised concern.

The findings from these various studies suggest that strong, sedating antihistamines may increase dementia risk when used long term, but newer allergy medications such as cetirizine do not. The main issue lies with the number of medications taken and for how long. People who take many drugs with anticholinergic effects are most at risk for memory problems over time.

Talking With Your Doctor

If you take allergy medicine regularly, it’s smart to discuss your medication choices with your doctor or pharmacist. This is especially true if you also take medications for sleep, pain, anxiety, or bladder problems.

Here are some helpful questions to ask:

• “Is my allergy medication the safest option for my age and health?”
• “Could I switch from an older medication like Benadryl to a newer one like Zyrtec or Claritin?”
• “Are there nondrug ways I could manage my allergies?”
• “Do any of my other prescriptions have anticholinergic effects?”

It’s important not to stop any medication suddenly without your doctor’s advice. Sometimes switching medications or reducing dosage can ease symptoms and lower risks.

Safer Allergy Management

Beyond medications, several simple steps can help manage allergy symptoms and reduce your need for antihistamines:

• Limit exposure to allergens. Keep windows closed during high pollen days, shower after being outdoors, and use an air purifier inside your home.
• Use nasal saline rinses. These can wash pollen and dust out of your nasal passages and provide relief without medication.
• Try nasal steroid sprays. They target inflammation directly and often reduce the need for oral antihistamines.
• Monitor your medications. If you take more than one drug with sedating or anticholinergic effects, talk to your doctor about alternatives.

Small changes like these can make a big difference in both your allergy control and your brain health.

Join the Conversation

On myALZteam, people share their experiences with Alzheimer’s disease, get advice, and find support from others who understand.

Do you have questions or concerns about antihistamines like Zyrtec and how they affect Alzheimer’s? Let others know in the comments below.