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Prolonged use or higher doses of certain common drugs is linked to an increased risk of dementia, including Alzheimer's disease, a new study found.

(The Oregonian files)

Prolonged use or higher doses of certain common drugs is linked to an increased risk of dementia, including Alzheimer's disease, a new study found.

The study, published Monday in Jama Internal Medicine, also unveiled evidence that the dementia risk persists even after the person stops taking the medication.

The drugs in question are what's called anticholinergic: They block a neurotransmitter in the centeral nervous system. They include antidepressants like doxepin (Sinequan), first-generation antihistamines like chlorpheniramine (Chlor-Trimeton), certain medications for bladder control, such as oxybutynin (Ditropan) and some sleeping pills.

"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," said Shelly Gray, director of the geriatric pharmacy program at the University of Washington. "They should tell their health care providers about all their over-the-counter use."

University of Washington researchers followed nearly 3,500 seniors more than seven years, tracking both their prescription medications and over-the-counter pills. The study found that people taking at least 10 milligrams a day of doxepin, 4 mg. of diphenhydramine or 5 mg. of oxybutynin for more than three years faced a greater dementia risk.

The study calculated hazard ratio, which is not the same as a risk factor that can be easily understood. The bottom line, Gray said, is that dementia is a common condition so any increased risk -- regardless of the factor -- is worrying, especially if there are alternative medications available.

Gray said patients should consider using alternative medications that are not anticholinergic. They include selective serotonin re-uptake inhibitors like citalopram -- Celexa -- or fluoxitene -- Prozac -- which are antidepressants. Second-generation antihistimines such as loratadine -- Claritin -- for allergies also are not anticholinergic.

She said if physicians prescribe anticholinergic drugs because they're the best option, they should give the lowest effective dose and stop when the drug is no longer needed.

When in doubt about over-the-counter drugs, ask a health care provider.

-- Lynne Terry

lterry@oregonian.com; 503-221-8503

@LynnePDX