Over-the-counter medicine linked to dementia
The US study did not include brand names but all medicines in the study were drugs that had an "anticholinergic" effect. Anticholinergic drugs block the action of the neurotransmitter acetylcholine.
Almost a fifth of the drugs could be purchased over the counter and included tricyclic antidepressants for treating depression, antihistamines used to treat allergies and hay-fever and antimuscarinics for treating urinary incontinence.
The study was led by Professor Shelly Gray, from the University of Washington School of Pharmacy in Seattle, and was reported in JAMA Internal Medicine.
Gray urged people not to stop their therapies but to talk to their doctor and to tell them about their over-the-counter drug use.
The seven-year study looked at 3,434 people aged 65 and older who had no signs of dementia when the research began. It looked at pharmacy and medical records to determine what drugs were taken by the participants. Over the seven years 797 participants developed dementia.
The researchers estimated that people taking at least 10mg of doxepin (an antidepressant) a day, four mg a day of diphenhydramine (to help them sleep) or five mg a day of oxybutynin (for urinary incontinence) for more than three years had a greater risk of developing dementia.
The recommended doctors and pharmacists offer different treatments where possible, or offer the lowest dose for the shortest possible time.