Taking commonly used medications with anticholinergic effects at higher doses or for prolonged periods has been found to increase the risk of dementia, including Alzheimer’s, according to a study conducted by US scientists.

Under the study published in JAMA Internal Medicine, many older people take these medications, which also include nonprescription diphenhydramine (Benadryl).

University of Washington (UW) professor and the first author of the report Shelly Gray said: "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.

"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."

Funded by the National Institute on Aging, Gray tracked around 3,500 Group Health seniors participating in a long-running joint Group Health-UW study.

"Older adults should be aware that many medications have strong anticholinergic effects."

Gray noted that anticholinergic effects happen because some medications block the neurotransmitter acetylcholine in the brain and body, which may cause side-effects such as drowsiness, constipation, retaining urine, and dry mouth and eyes.

Tricyclic antidepressants such as doxepin (Sinequan), first-generation antihistamines such as chlorpheniramine (Chlor-Trimeton), and antimuscarinics for bladder control such as oxybutynin (Ditropan) are the medications used in the study.

The study revealed that older people taking at least 10mg/day of doxepin, 4mg/day of chlorpheniramine, or 5mg/day of oxybutynin for more than three years found to be at greater risk for developing dementia.

Acording to Gray, substitutes are available for the first two, which include a selective serotonin re-uptake inhibitor (SSRI) such as citalopram (Celexa) or fluoxitene (Prozac) for depression and a second-generation antihistamine such as loratadine (Claritin) for allergies.

The study was supported by National Institute on Aging NIH Grants and Branta Foundation.

Image: University of Washington professor and the study’s lead author Shelly Gray. Photo: courtesy of University of Washington.