A new study shows definitive proof that popular over-the-counter allergy medications can cause serious side effects to users' brain functions.

CNN reports that the new study out of the Indiana University of School of Medicine found that common medications such as Benadryl, Demerol, Dimetapp and others all contain anticholinergic drugs that are linked to cognitive impairment and increased risk of dementia.

The university study examined physical changes to the brain of patients who use the drugs. It was found that the medications lowered metabolism and reduced brain sizes.

Tests performed revealed those those taking the drugs in question performed worse in short-term memory tests than those who didn't take the medications.

The study examined 451 people with an average age of 73, sixty of whom were taking at least one of the targeted medications.