Story highlights Anticholinergic drugs have been linked to cognitive impairment and increased risk of dementia

A new study finds lower metabolism and reduced brain sizes in participants taking these drugs

(CNN) From allergies to insomnia, there's a pill for just about every problem. The problem is, those pills often come with a lengthy list of potential side effects.

And in the quest to cure what ails us as quickly as possible, those warnings are too often overlooked.

A new study, published Monday, offers the most definite proof yet of what scientists have known for at least a decade: that anticholinergic drugs (PDF) are linked with cognitive impairment and an increased risk of dementia.

Though you may have never heard of this class of drug, you've certainly heard of the medications themselves, including Benadryl, Demerol, Dimetapp, Dramamine, Paxil, Unisom and VESIcare. They are sold over the counter and by prescription as sleep aids and for chronic diseases including hypertension, cardiovascular disease and chronic obstructive pulmonary disease (COPD).

The new study is the first to examine the physical changes that serve as the catalyst for cognitive decline. Using brain imaging techniques, researchers at the Indiana University School of Medicine found (PDF) lower metabolism and reduced brain sizes among study participants taking anticholinergic drugs.

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