Another study, published online April 18 by JAMA Neurology, serves as a reminder that over-the-counter medications sold to treat colds, sleep issues, heartburn, allergies or diarrhea may come with a side effect: cognitive impairment. That’s because the drugs have an anticholinergic effect.

Scientists have known about the link between between the drugs and cognitive impairment and increased risk of dementia for at least 10 years, with cognitive problems often occurring when the drugs have been taken continuously for 60 to 90 days. The new paper, published by a team led by scientists at the Indiana University School of Medicine, Indianapolis, however, is believed to be the first to address the potential underlying biology of those links through 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 Shannon Risacher, Ph.D., an assistant professor of radiology and imaging sciences and first author of the paper.

The current research project involved 451 participants drawn from the Alzheimer’s Disease Neuroimaging Initiative and the Indiana Memory and Aging Study. Sixty of them were taking at least one medication with anticholinergic activity deemed to be medium or high.

Researchers assessed the results of memory and other cognitive tests, positron emission tests measuring brain metabolism and magnetic resonance imaging scans for brain structure. They found:

  • People taking anticholinergic drugs 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.
  • Those who used anticholinergic drugs also showed lower brain activity in both the overall brain and in the hippocampus, a region associated with memory and which has been identified as affected early by Alzheimer’s disease.
  • Study participants taking anticholinergic drugs had reduced brain volume and larger cavities inside the brain.

In light of the study’s findings, Risacher echoed previous advice, saying: “Given all the research evidence, physicians might want to consider alternatives to anticholinergic medications if available when working with their older patients.”

In addition to some OTC medications, some prescriptions for chronic diseases such as hypertension, cardiovascular disease and chronic obstructive pulmonary disease also have anticholinergic effects, according to the researchers. A list of anticholinergic drugs and their potential effects is available online.