If it doesn’t have side effects, it isn’t a drug, so goes the saying.
But you would think that widely used medications for colds and allergies – including many that are available without a prescription – would be relatively harmless.
According to a growing body of research, they are anything but.
A class of drugs called anticholinergics have been linked to cognitive impairment in past studies, and new research provides more evidence of an association.
The new study, published in JAMA Neurology, found that older people who regularly took at least one anticholinergic drug showed poorer cognition, lower brain volumes and less glucose metabolism in the whole brain and the temporal lobe, (which is important for memory) than people who didn’t report taking this kind of medications. The link persisted even after the team controlled for the number of medications the people in the study were taking.
These medicines interfere with the ability of a crucial brain chemical called acetylcholine (Ach) to attach to nerve cells. ACh is essential for muscle contraction. Acetylcholine is also critical for proper brain function. Without ACh doing its job transmitting messages between brain cells, you would become forgetful and confused.
Anticholinergic drugs include certain over-the-counter medications like Benadryl, Tylenol PM, and Advil PM, and prescribed medications like some antidepressants, motion sickness medications, and bladder control drugs.
For this study, researchers used brain imaging techniques and found lower metabolism and reduced brain sizes among study participants taking the drugs.
Previous research found a link between between the anticholinergic drugs and cognitive impairment, worsened memory, and increased risk of dementia. The new study is believed to be the first to explore the potential underlying biology of those clinical links using neuroimaging measurements of brain metabolism and atrophy.
Shannon Risacher, Ph.D., assistant professor of radiology and imaging sciences, first author of the paper, said of the study:
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,
Given all the research evidence, physicians might want to consider alternatives to anticholinergic medications if available when working with their older patients.
Drugs with anticholinergic effects are sold over the counter and by prescription as sleep aids and for many chronic diseases including hypertension, cardiovascular disease, and chronic obstructive pulmonary disease.
A list of anticholinergic drugs can be found here: Where Can I Find A List of Anticholinergic Drugs?
Scientists have linked anticholinergic drugs cognitive problems among older adults for at least 10 years. A 2013 study by scientists at the IU Center for Aging Research and the Regenstrief Institute found that drugs with a strong anticholinergic effect cause cognitive problems when taken continuously for as few as 60 days. Drugs with a weaker effect could cause impairment within 90 days.
The current research project involved 451 participants, 60 of whom were taking at least one medication with medium or high anticholinergic activity. The participants were drawn from a national Alzheimer’s research project – the Alzheimer’s Disease Neuroimaging Initiative – and the Indiana Memory and Aging Study.
To identify possible physical and physiological changes that could be associated with the reported effects, researchers assessed the results of memory and other cognitive tests, positron emission tests (PET) measuring brain metabolism, and magnetic resonance imaging (MRI) scans for brain structure.
The cognitive tests revealed that patients 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.
Anticholinergic drug users also showed lower levels of glucose metabolism – a biomarker for brain activity – in both the overall brain and in the hippocampus, a region of the brain associated with memory and which has been identified as affected early by Alzheimer’s disease.
The researchers also found significant links between brain structure revealed by the MRI scans and anticholinergic drug use, with the participants using anticholinergic drugs having reduced brain volume and larger ventricles, the cavities inside the brain.
Dr. Risacher said,
I certainly wouldn’t advise my grandparents or even my parents to take these medications unless they have to.
I’d suggest that doctors monitor medications and their effects, and to use the lowest dose that’s effective.
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.