Researchers have discovered a significant link between high use of anticholinergic drugs – including popular non-prescription sleep aids and the antihistamine Benadryl (diphenhydramine) – and increased risk of developing dementia and Alzheimer’s disease in older people. Share on Pinterest Many medications – including some popular over the counter drugs – have strong anticholinergic effects. Anticholinergics are a class of drug that blocks the action of the neurotransmitter acetylcholine in the brain and body. This can lead to many side effects, including drowsiness, constipation, retaining urine and dry mouth and eyes. The researchers, led by Shelly Gray, a professor in the University of Washington School of Pharmacy in Seattle, reported their findings in JAMA Internal Medicine in January 2015. Prof. Gray says: “Older adults should be aware that many medications – including some available without a prescription, such as over-the-counter sleep aids – have strong anticholinergic effects.”

People should not stop their therapy but talk to their health care provider Prof. Gray urges people not to stop their therapy based on the findings of this study – they should talk to their health care provider, and also tell them about all their over-the-counter drug use. “Health care providers should regularly review their older patients’ drug regimens – including over-the-counter medications – to look for chances to use fewer anticholinergic medications at lower doses,” she says. If providers need to prescribe anticholinergics to their patients because they offer the best treatment, then “they should use the lowest effective dose, monitor the therapy regularly to ensure it’s working, and stop the therapy if it’s ineffective,” she adds. Although the link between raised risk of dementia and anticholinergics has been found before, the new study uses more rigorous methods – including over 7 years of follow-up – to establish the strength of the link. By accessing pharmacy records, the researchers were also able to include non-prescription use of anticholinergics in their data. It is also the first study to show a dose-response effect, note the authors. That is, the higher the cumulative amount of drug taken, the higher the risk of developing dementia. And another first for the study, is that it also shows that dementia risk linked to anticholinergics may persist long after people stop taking the drugs.