Taking some commonly prescribed medicines, including insomnia treatments, could increase the risk of dementia, a new study suggests.
These medications are ones that have anticholinergic effects, including sleeping medication Nytol and anti-allergy pills Benadryl and Piriton. They are commonly taken by older people.
Anticholinergic medications block a neurotransmitter known as acetylcholine in the brain and body. That can cause many side effects, including drowsiness, constipation, urinary retention, and dry mouth and eyes.
Researchers at the University of Washington found that the risks were present when high doses of the medicines were taken. They are likely to persist and remain irreversible for several years after people stop taking the drugs.
The most common medications studied were tricyclic antidepressants like doxepin (Sinequan), first-generation antihistamines like chlorpheniramine (Chlor-Trimeton), and antimuscarinics for bladder control like oxybutynin (Ditropan).
People taking at least 10 mg/day of doxepin, 4 mg/day of chlorpheniramine, or 5 mg/day of oxybutynin for more than three years would be at greater risk of developing dementia, according to the study, which is published in JAMA Internal Medicine.
For those taking the highest doses of the drugs over the study period, the risk of dementia was 54 per cent higher than those using none. The risk of Alzheimer's was 63 per cent higher.
Professor Shelly Gray, the first author of the report, recommended that doctors prescribe the lowest dose of the treatments, monitor them continually and stop them if they prove to be ineffective.
"No one should stop taking any therapy without consulting their health care provider," she added. Healthcare providers should regularly review their older patients' drug regimens, including over-the-counter medications, to look for chances to use fewer anticholinergic medications at lower doses."
The study followed nearly 3,500 Group Health seniors participating in a long-running joint Group Health-UW study funded by the National Institute on Aging.
Some of the participants have agreed to a brain autopsy after they die, allowing the scientists to conduct follow-up research.
Read more about Barchester's dementia care homes.