Can Chronic Medication Use Cause Dementia?

A new research study published in the Journal of the American Medical Association- Internal Medicine suggests that prolonged use of certain common medications, including antihistamines and sleep remedies, by older adults increases the risk of developing dementia.  Conducted by Dr. Shelley Gray of the University of Washington and a team of fellow researchers, the study focused on anti-cholinergic medications and the potential role they played in patients later developing dementia, including Alzheimer's disease.

Anti-cholinergic medications block the neurotransmitter acetycholine in the human nervous system.   They are often prescribed to treat gastrointestinal disorders such as gastritis and diarrhea, urinary disorders such as urethritis, respiratory disorders, insomnia, and motion sickness symptoms.  Among the different anti-cholinergic medications that are commonly prescribed to patients over the age of sixty are:  diphenhydramine (Benadryl), dimenhydrinate (Dramamine), buproprion (Zyban, Welbutrin), scopolamine, antihistamines, and certain anti-depressants such as Sinequan.   While medical researchers have already recognized possible cognitive problems in older adults taking these medications, it was previously assumed that these problems would end when the medication was discontinued.

Dr. Gray and her fellow researchers examined more than three thousand seniors in the Seattle, Washington area over a seven-year period and found a clear dose-response relationship between taking high doses of anti-cholinergic medication over a prolonged time period and dementia.  For example, patients taking at least ten mg per day of doxepin (Sinequan), four mg. per day of the antihistamine chlorpheniramine, or five mg per day of oxybutynin (to treat bladder problems) for more than three years would have an increased  risk for developing dementia.  

The researchers found that 637 participants (18.5 per cent) had developed Alzheimer’s disease over the seven years they were followed in the study. An additional 160 (4.6 per cent) had developed other forms of dementia.   By comparison, the Alzheimer's Society of Canada reports that about fifteen percent of adults over the age of sixty-five are living with some form of dementia.

"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," Dr. Gray said in a media statement.   She also recommends that older adults should tell their doctors about all the different medications they are taking, including over-the-counter medications, and that health providers review these medications with their older patients to cut down on anticholinergic use.

“Our findings suggest that a person taking an anticholinergic, such as oxybutynin chloride, 5 mg/d, ordoxepin hydrochloride, 10mg/d, for more than 3 years would have a greater risk for dementia,” the authors of the study wrote in their conclusions. “Prescribers should be aware of this potential association when considering anticholinergics for their older patients and should consider alternatives when possible.”

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