GPs and pharmacists should make the risks clear to patients who are taking these drugs, the researchers warned.
The study looked at use of prescription and over-the-counter drugs, such as hayfever medication, antidepressants and sleep aids, in people over 65 years old.
They found that higher doses of the drugs, and use over a long period of time, were linked to a higher risk of dementia. People that had stopped taking anticholinergics for up to seven years still had an increased risk of dementia, suggesting that the effect cannot be reversed.
‘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,’ said Professor Shelly Gray, from the University of Washington, who led the study.
‘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.’
Dementia risk was heightened in people who took 10mg of doxepin (Sinequan), 4mg of diphenhydramine (Benadryl), or 5mg of oxybutynin (Ditropan) every day for more than three years.
The researchers recommend that doctors prescribe or recommend substitutes for these drugs, such as citalopram or loratadine.