A US study in the journal JAMA Internal Medicine has linked commonly used medicines, including over-the-counter treatments for conditions such as insomnia and hay-fever, to higher dementia risk in elderly people taking the drugs every day for three years or more.
Michelle Roberts, Health editor, BBC News:
Dr Shelly Gray and colleagues from the University of Washington followed the health of 3,434 people aged 65 and older who had no signs of dementia at the start of the study.
They looked at medical and pharmacy records to determine how many of the people had been given a drug with an anticholinergic effect, at what dose and how often and compared this data with subsequent dementia diagnoses over the next decade.
The most commonly used anticholinergic-type drugs were medicines for treating depression, antihistamines for allergies such as hay-fever or to aid sleep/promote drowsiness, and drugs to treat urinary incontinence. Nearly a fifth were drugs that had been bought over the counter.
Over the course of the study, 797 of the participants developed dementia.
The study estimated that people taking at least 10 mg/day of doxepin (antidepressant), four mg/day of diphenhydramine (a sleep aid), or five mg/day of oxybutynin (a urinary incontinence drug) for more than three years would be at greater risk of developing dementia.
The researchers say doctors and pharmacists might want to take a precautionary approach and offer different treatments instead. And when there is no alternative, they could give the lowest dose for the shortest time possible.