The drugs, which are regularly prescribed as antidepressants and to treat incontinence, increase dementia risk even when taken 20 years before diagnosis of cognitive impairment.
Researchers at The University of East Anglia in the United Kingdom studied the medical records of more than 40,000 patients aged 65 and older with dementia, and compared them to records of more than 283,000 people without the ailment.
Rob Howard, professor of old age psychiatry at University College London, said: "It is possible that use of some of these drugs may have actually been to treat the very earliest symptoms of Alzheimer's disease, which can be associated with low mood and lower urinary tract infections, many years before the development of dementia".
Some other anticholinergic medicines that are used for treating hay fever, travel sickness, and stomach cramps are not connected with the increase of risk in dementia.
This is the largest and most detailed study of its kind into the long-term impact of anticholinergic use in relation to dementia.
"We already have strong evidence that anticholinergics cause confusion and in the short-term will potentially worsen the symptoms of dementia", said co-author Ian Maidment, PhD, of Aston University in Birmingham, England, in a statement. Researchers compared how many daily doses of anticholinergic drugs these patients had been prescribed between four and 20 years earlier with a control group of nearly 300,000 matched individuals.
"We studied patients with a new dementia diagnosis and looked at what anticholinergic medication they were prescribed between four and 20 years prior to being diagnosed". These lifestyle factors are associated with a 40% to 60% increased risk of developing dementia, according to a 2017 study. Of the controls, 30 percent were prescribed at least one anticholinergic drug; of the cases, 35 percent were.
Frequently prescribed anticholinergic drugs include procyclidine (Kemadrin) for Parkinson's; tolterodine, oxybutynin, and solifenacin (Vesicare) for urological conditions such as overactive bladder or incontinence; and amitriptyline, dosulepin, and paroxetine for depression.
The study also analyzed over 27 million prescriptions.
"There are robust associations between levels of anticholinergic antidepressants, antiparkinsons, and urologicals and the risk of a diagnosis of dementia up to 20 years after exposure", they wrote.
Anticholinergic drugs block chemical signals to the brain that control muscle movements. This means that some, but not all, anticholinergic drugs were implicated.
Experts on dementia and Alzheimer's disease urged patients to be cautious about the results of the study, the BBC said.
George Savva from the School of Health Sciences of the University of East Anglia reported that, "This research is really important because there are an estimated 350 million people affected globally by depression".
"This study shows that some anticholinergics may cause long-term harm in addition to short-term harm".
To examine these associations, researchers used multiple conditional logistic regression to evaluate patients with a new diagnosis of dementia and compared their anticholinergic drug use 4-20 years before diagnosis; they were then matched to a control group without dementia. "Further research is needed to understand possible reasons for this link".