Many people don't realize that some of the most commonly used over-the-counter medications — often taken for allergies, sleep, or motion sickness — may interfere with short-term memory.

Research suggests these drugs can also raise the risk of dementia, with older adults particularly vulnerable to their effects.

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Dr. Gary Small, brain health expert and chair of psychiatry at Hackensack University Medical Center in New Jersey, said this issue deserves attention.

"This is an important issue because many people take over-the-counter medicines for sleep, drugs like Sominex, Tylenol PM, or for allergies like Benadryl," Small told Newsmax's "National Report." "And they contain a compound called diphenhydramine."

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Diphenhydramine is an antihistamine that causes drowsiness and dries up nasal passages, which is why it's commonly found in sleep aids and allergy medications. But those same effects can come with a downside.

"Now it makes you sleepy and it clears up your sinuses, but it also can cause memory loss. And this is a big problem for older people who are already struggling with forgetfulness. And as you say, it can cause an increased risk for dementia over time," said Small, editor of Dr. Gary Small's Mind Health Report.

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Health experts caution that while occasional use may be unavoidable, frequent or long-term use — especially in older adults — should be discussed with a healthcare provider. Safer alternatives may be available that don't carry the same cognitive risks.

Protecting memory isn't just about avoiding harmful substances — it's also about adopting habits that support long-term brain health, according to Small, who is also the physician in chief for Behavioral Health Services at Hackensack Meridian Health.

His book, "The Memory Bible," focuses on practical strategies to help people stay mentally sharp, informed, and proactive as they age.