It's allergy season and many of us will be reaching into the medicine cabinet for relief. But it is important to choose wisely, as some allergy medications can harm brain health and increase dementia risk.
Diphenhydramine (e.g., Benadryl®) is a first-generation antihistamine medication . In addition to treating allergy and cold symptoms such as sneezing and watery eyes, it also blocks the actions of acetylcholine. This is a neurotransmitter that is important for brain functions including learning and memory. Diphenhydramine is classified as an anticholinergic drug, and a study of this class of drug found that increased use is associated with an up to 54% increased risk of dementia .
In the short-term, side effects of diphenhydramine can include dizziness, drowsiness, confusion, blurred vision, sedation, difficulty urinating, constipation, and low blood pressure . Multiple high-quality human trials have shown that diphenhydramine impairs cognitive functions such as alertness , attention , memory , executive function , reaction time , and vigilance . These studies also reported that diphenhydramine increased fatigue and sleepiness while decreasing motivation . An observational study of older hospitalized patients reported that diphenhydramine treatment significantly increased risk for delirium symptoms, including inattention, disorganized speech, and altered consciousness . Older adults with kidney or liver impairment are especially prone to these adverse effects . In fact, diphenhydramine is listed as inappropriate on the Beer's Criteria for Potentially Inappropriate Medication Use in Older Adults .
The good news is that newer antihistamines equal the effectiveness of diphenhydramine with few or no cognitive side effects. These medications were developed to minimize adverse events common to diphenhydramine and other older antihistamines .
If you're older or have concerns about brain health, consider an allergy medication other than diphenhydramine. In addition to the medications above, topical nasal sprays and allergy shots are available by prescription and can also help alleviate symptoms. As always, it's a good idea to discuss your options with a medical professional.
Yuko Hara, PhD, is Director of Aging and Alzheimer's Prevention at the Alzheimer's Drug Discovery Foundation. Dr. Hara was previously an Assistant Professor in Neuroscience at the Icahn School of Medicine at Mount Sinai, where she remains an adjunct faculty member. Her research focused on brain aging, specifically how estrogens and reproductive aging influence the aging brain's synapses and mitochondria. She earned a doctorate in neurology and neuroscience at Weill Graduate School of Medical Sciences of Cornell University and a bachelor's degree in biology from Cornell University, with additional study at Keio University in Japan. Dr. Hara has authored numerous peer-reviewed publications, including articles in PNAS and Journal of Neuroscience.
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