Q. Is it OK to take Benadryl every day to treat my allergies?

A. It’s not a good idea. Benadryl Allergy (diphenhydramine and generic) and similar first-generation antihistamines used to treat allergy symptoms, such as chlorpheniramine (Chlor-Trimeton Allergy and generic), shouldn’t be taken for long periods of time. Besides having side effects including drowsiness, confusion, and urinary retention, a new study shows that frequent, long-term use of older antihistamines are associated with an increased risk of dementia and Alzheimer’s disease.

The study found that also to be true for certain drugs used to treat depression, asthma, overactive bladder, and Parkinson’s. Those types of drugs are known as anticholinergics, and they block the substance acetylcholine, which is involved in learning, memory, and muscle contractions.

The study, published online in the Journal of the American Medical Association (JAMA) in January, looked at 10 years' worth of pharmacy data, including prescription and over-the-counter drugs, taken by 3,434 adults age 65 or older who didn’t have dementia at the beginning of the study. Researchers at the University of Washington School of Pharmacy then tracked them for about seven years. During that time, 797 participants (23 percent) developed dementia.

Researchers found that people who had regularly taken any type of anticholinergic, including the older antihistamines like chlorpheniramine and diphenhydramine, were more likely to develop the disease than those who had not, and those who’d taken the drugs for three years or more had an even higher risk.

Learn more about allergy treatments in our CR Best Buy Drugs Antihistamines Report.

While additional research is needed, the study’s findings and several previous studies suggest an association between taking older antihistamines over a period of time and cognitive decline, particularly in older adults.

If you need an allergy medicine, consider a newer, “second-generation” antihistamine like our Best Buy picks loratadine (Claritin and generic), or cetirizine (Zyrtec and generic)—though don't take either for longer than you need to. Those newer antihistamines, our analysis shows, are equally as effective at reducing allergy symptoms than the older ones, and have fewer side effects, namely drowsiness. They also appear to have a lower risk of causing memory problems.

Some people respond better to one of the newer antihistamines over others, so some trial and error may be necessary. Preventive measures, such as staying indoors when the pollen count is high and washing your hands and face after spending time outdoors, can also help.

—Ginger Skinner

These materials were made possible by a grant from the state Attorney General Consumer and Prescriber Education Grant Program, which is funded by a multistate settlement of consumer fraud claims regarding the marketing of the prescription drug Neurontin (gabapentin).

More from Consumer Reports:
It’s time to buy a new phone, here’s why
Dos and don’ts of itemized tax deductions
Top 5 ways to boost the value of your home

Consumer Reports has no relationship with any advertisers on this website. Copyright © 2006-2015 Consumers Union of U.S.

n