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Shannon Risacher is the lead author of a study that links common over-the-counter drugs and dementia.

(Courtesy of Indiana University School of Medicine)

Over-the-counter nighttime cold medicines can make life bearable when you're battling a virus. And for allergy sufferers, drugs like Benadryl can significantly improve quality of life.

But researchers at Indiana University School of Medicine now suggest you think long and hard before taking many common cold and allergy medications, especially if you're past middle age.

The scientists, whose work has been published in the journal JAMA Neurology, say drugs that have a strong "anticholinergic effect" shrink the brain and decrease brain metabolism. This is not a new finding: earlier research has found a link between anticholinergic drugs and cognitive impairment among older adults. A 2013 study concluded that taking one of these drugs for only two months causes memory problems in older people.

The new academic paper, reports Indiana University, "is believed to be the first to study the potential underlying biology of those clinical links using neuroimaging measurements of brain metabolism and atrophy."

"These findings provide us with a much better understanding of how this class of drugs may act upon the brain in ways that might raise the risk of cognitive impairment and dementia," said study lead author Shannon Risacher, who's an assistant professor of radiology and imaging sciences at Indiana University School of Medicine. "Given all the research evidence, physicians might want to consider alternatives to anticholinergic medications if available when working with their older patients."

"I certainly wouldn't advise my grandparents or even my parents to take these medications unless they have to," Risacher says.

* Check out a guide to common medicines that have anticholinergics.

Study participants taking anticholinergic drugs had lower levels of glucose metabolism, which is a "biomarker" indicating brain activity and Alzheimer's disease, Indiana University reports. They also performed "worse than older adults not taking the drugs on short-term memory and some tests of executive function, which cover a range of activities such as verbal reasoning, planning and problem solving."

The 451 participants, all between the ages of 70 and 75, underwent MRI scans, and those using anticholinergic drugs had "reduced brain volume."

Dr. Risacher says the results provide "clues" to the biological impact of these drugs on the brain but pointed out that "additional studies are needed if we are to truly understand the mechanisms involved."

* Read the study.

-- Douglas Perry