Anticholinergic medications span a range of common drugs and include antihistamines, sleep aids, antidepressants, cardiovascular meds, gastrointestinal drugs (for diarrhea, incontinence, diverticulitis, and ulcers), and muscle relaxants. Now, a new study confirms the link between these everyday medications and dementia. Taking anticholinergic drugs at high doses or for a long time may significantly increase your risk for developing Alzheimer's disease and other dementias, say researchers from University of Washington School of Pharmacy.

“If providers need to prescribe a medication with anticholinergic effects because it is the best therapy for their patient, they should use the lowest effective dose, monitor the therapy regularly to ensure it's working, and stop the therapy if it's ineffective,” Dr. Shelly Gray, a professor and director of the geriatric pharmacy program at the UW School of Pharmacy said in a release.

On average, older people take four or five prescription drugs and two over-the-counter drugs each day. Clearly, drugs are an important part of medical care for older people; however, older people are more sensitive to the effects of many pills, including anticholinergics, which block the neurotransmitter acetylcholine and so effect the nervous system. While the drugs are too numerous to mention, those with anticholinergic effects — and these effects are sometimes dependent on the dose include Benadryl, Sominex, Xanax, Ativan, Valium, Luminal, Skelaxin, Limbitrol, and Tavist.

For the current study, the researchers investigated a previously reported link between anticholinergics, both prescription strength and over-the-counter, and dementia by employing more rigorous methods than in the past. Specifically, the researchers conducted a longer follow-up of more than seven years and more accurate use assessment via pharmacy records, which included nonprescription choices. The team tracked nearly 3,500 seniors participating in a long-running study, the Adult Changes in Thought (ACT), a joint project of UW and the National Institute on Aging.

The most commonly used medications in the study, the researchers discovered, were tricyclic antidepressants like doxepin (Sinequan), antihistamines like chlorpheniramine (Chlor-Trimeton), and antimuscarinics for bladder control like oxybutynin (Ditropan). People taking at least 10 mg/day of doxepin, 4 mg/day of diphenhydramine, or 5 mg/day of oxybutynin for more than three years, the researchers estimated, would be at greater risk for developing dementia. Importantly, substitutes are available for some of these drugs.  

While this study is the first to show a dose response — meaning, the more you use anticholinergic medications the greater your risk of developing Alzheimer’s — it also is the first to suggest this higher risk may persist, and may not be reversible, even years after you stop taking these drugs. “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,” Gray said.

Source: Gray S, Crane P, Dublin S, et al. Cumulative Use of Strong Anticholinergic Medications and Incident Dementia. JAMA Internal Medicine. 2015.