You can treat just about any ailment with over-the-counter medicine — from pain relievers to cold and allergy treatments. However, in our hastiness to get rid of or minimize our health problems, it’s easy to overlook the side effects that come with these miracles in a bottle, some more serious than others. One such side effect is cognitive impairment in older adults who take common OTC medicines, a new study published in JAMA Neurology suggests.  

Led by scientists at the Indiana University School of Medicine, the study examined the association between anticholinergic medication and cognition in “cognitively normal” older adults — people aged 65 and older without Alzheimer’s disease or dementia. Researchers found that this class of drug, used to treat diseases like asthma, cramps, insomnia and allergies, could contribute to brain shrinkage and to low glucose metabolism, which is critical for brains.

“I certainly wouldn’t advise my grandparents or even my parents to take these medications unless they have to,” Dr.  Shannon Risacher, first author of the paper, told Time after learning about these associations.

Although this class of drug may sound unfamiliar, it’s highly likely that you’ve heard of or even used the medications, which include Benadryl, Thorazine, and Zantac. The current study builds on past research linking anticholinergic drugs with cognitive impairment and an increased risk of dementia.

"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 Risacher, assistant professor of radiology and imaging sciences, in a statement.

For the study, researchers looked over data from the Alzheimer's Disease Neuroimaging Initiative and the Indiana Memory and Aging Study. All together, they analyzed records from 451 participants, 60 of whom were taking at least one medication with medium-to-high anticholinergic activity regularly. Participants’ memory and cognitive functions, as well as brain structure, were measured with PET and MRI scans.

Results revealed that older adults who took anticholinergic drugs performed worse on short-term memory tests as well as some executive function tests, which cover a range of activities such as verbal reasoning, planning, and problem solving. Anticholinergic drug users also had lower levels of glucose metabolism in both the overall brain and in the hippocampus, a region of the brain thought to be the center of emotion and memory. The MRI scans revealed that people taking these drugs also had reduced brain volume.

"These findings might give us clues to the biological basis for the cognitive problems associated with anticholinergic drugs, but additional studies are needed if we are to truly understand the mechanisms involved," Risacher said.

Beyond the small sample size, study limitations included the inability to determine causality with the findings. Low glucose metabolism and brain shrinkage may have been due to poor health rather than anticholinergic drug use. For this reason, Risacher said larger studies that have “better-controlled medication history assessment” will be needed.

Source: Risacher S, McDonald B, Tallman, et al. Association Between Anticholinergic Medication Use and Cognition, Brain Metabolism, and Brain Atrophy in Cognitively Normal Older Adults. JAMA Neurology. 2016.