Commonly prescribed drugs may increase risk of dementia, study says

Risk for dementia may increase with long-term use of some commonly prescribed medications, according to a new study published in JAMA Internal Medicine.

The study, carried out by experts from the University of Nottingham and funded by the NIHR School for Primary Care Research, found that there was nearly a 50 percent increased risk of dementia among patients aged 55 and over who had used strong anticholinergic medication daily for three years or more.

Anticholinergic drugs help to contract and relax muscles. They work by blocking acetylcholine, a chemical that transmits messages in the nervous system. Doctors prescribe the drugs to treat a variety of conditions, including chronic obstructive pulmonary disease, bladder conditions, allergies, gastrointestinal disorders, and symptoms of Parkinson's disease. These medicines can have short-term side effects, including confusion and memory loss, but it is less certain whether long-term use increases the risk of dementia, researchers said.

Led by Carol Coupland, PhD, from the university's Division of Primary Care, researchers looked at the medical records of 58,769 patients with a diagnosis of dementia and 225,574 patients without a diagnosis of dementia, all aged 55 and over and registered with U.K. GPs contributing data to the QResearch database, between January 1, 2004 and January 31, 2016.

The study findings showed increased risks of dementia for anticholinergic drugs overall and specifically for the anticholinergic antidepressants, antipsychotic drugs, anti-Parkinson’s drugs, bladder drugs, and epilepsy drugs after accounting for other risk factors for dementia. No increased risks were found for the other types of anticholinergic drug studied such as antihistamines and gastrointestinal drugs, according to the study abstract.

The 58,769 patients with dementia had an average age of 82 years old and 63 percent were women. Each dementia case was matched to five control patients of the same age, sex, and general practice.

Anticholinergic drug exposure was assessed using prescription information over a complete period of 10 years from one to 11 years before diagnosis of dementia or the equivalent dates in control patients and was compared between the two patient groups. Further analysis looked at prescriptions for anticholinergic drugs up to 20 years before diagnosis of dementia.

In the 1-11 years before the dementia diagnosis date or equivalent in controls, nearly 57 percent of cases and 51 percent of controls were prescribed at least one strong anticholinergic drug, with an average of six prescriptions in cases and four in controls. The most frequently prescribed types of drugs were antidepressants, anti-vertigo, and bladder antimuscarinic drugs, which are used to treat an overactive bladder.

The increased risk associated with these drugs indicates that if the association is causal around 10 percent of dementia diagnoses could be attributable to anticholinergic drug exposure, researchers said. This is comparable with other modifiable risk factors for dementia, including 5 percent for midlife hypertension, 3 percent for diabetes, 14 percent for later life smoking and 6.5 percent for physical inactivity.

This is an observational study so no firm conclusions can be drawn about whether these anticholinergic drugs cause dementia, and it is possible that the drugs were being prescribed for very early symptoms of dementia, Coupland said.

“Our study adds further evidence of the potential risks associated with strong anticholinergic drugs, particularly antidepressants, bladder antimuscarinic drugs, anti-Parkinson drugs and epilepsy drugs,” she said. “The risks of this type of medication should be carefully considered by healthcare professionals alongside the benefits when the drugs are prescribed and alternative treatments should be considered where possible, such as other types of antidepressants or alternative types of treatment for bladder conditions.”