We're in the midst of sneezing, sniffling, itchy eye season, but you still may want to think twice about popping a pill to soothe your allergy symptoms.
A 2016 study confirms what researchers have been investigating for more a decade: Anticholinergic drugs are linked with cognitive impairment and an increased risk of dementia. Anticholinergics are a class of drugs that include over-the-counter and prescription medications used to treat allergies and asthma, as well as sleep disorders and depression, reported Healthline. They may also be prescribed for incontinence, gastrointestinal cramps and muscular spasms, as well as high blood pressure, chronic obstructive pulmonary disease (COPD) and symptoms of Parkinson's disease.
You may not recognize the name of the class of drugs, but you likely know some of the brands: Benadryl, Dimetapp and Unisom, for example. Here's a full list of anticholinergics if you want to understand what's in your medicine cabinet. (Editor's note: The link in the last sentence was not working earlier, but it has been replaced.)
Another study released in 2018 reaffirms the previous study and shows that people who suffered from Parkinson's disease, urinary incontinence and depression and took anticholinergic drugs for at least a year developed a 30 percent increased risk of developing dementia later in life. Researchers also looked at the different classes of anticholinergic drugs to determine if some may not necessarily lead to risk in dementia.
"Of particular interest to us is the classes where there is no association. Previously, antihistamines have been implicated (in dementia risk), but we've not found any association between those specifically and dementia, as well as the gastrointestinal drugs," the study's lead author George Savva said.
Although researchers have known about the link for some time, this is the first time neuroimaging methods have helped determine the cognitive changes associated with the medications. Researchers at the Indiana University School of Medicine used brain imaging techniques to look for the physical changes associated with these drugs. They studied more than 400 adults with an average age of 73 by giving them a series of neuropsychological tests and cognitive questionnaires, followed by PET scans and MRIs.
Study participants who were taking anticholinergic medications performed more poorly on cognitive tests, particularly in immediate memory recall and executive functioning.
Those people in the study who used anticholinergic drugs also had lower levels of glucose metabolism, which is a strong marker of brain function.
"The use of AC medication was associated with increased brain atrophy and dysfunction and clinical decline," the researchers concluded in the study, which was published in the Journal of the American Medical Association. "Thus, use of AC medication among older adults should likely be discouraged if alternative therapies are available."
An earlier study found drugs that have a strong anticholinergic impact can have an effect on the brain after just 60 days of use. Drugs with a weaker impact can still have a cognitive effect after 90 days.
But should you tough out allergy season without drugs? That's a question for another study.
Editor's note: This article has been updated since it was originally published in April 2016.