A statistical correlation showed nearly a 50 percent increased risk of dementia among patients aged 55 and over who had used strong anticholinergic medication to contract and relax muscles  daily for three years or more. 

Anticholinergic drugs work by blocking acetylcholine, a chemical that transmits messages in the nervous system and is prescribed to treat a variety of conditions, including chronic obstructive pulmonary disease, bladder conditions, allergies, gastrointestinal disorders and symptoms of Parkinson's disease. Though they can have short-term side effects, including confusion and memory loss, there has been no scientific evidence that long-term use increases the risk of dementia.

A new paper in JAMA Internal Medicine does not provide scientific evidence but it is exploratory statistics distilled from the medical records of 58,769 patients with a diagnosis of dementia and 225,574 patients without a diagnosis of dementia, all aged 55 and over and registered with UK GPs contributing data to the QResearch database, between 1 January 2004 and 31 January 2016. The concluded there were increased risks of dementia for anticholinergic drugs overall and specifically for the anticholinergic antidepressants, antipsychotic drugs, antiparkinsons drugs, bladder drugs and epilepsy drugs after accounting for other risk factors for dementia. 

No increased risks were found for the other types of anticholinergic drug studied such as antihistamines and gastrointestinal drugs.

The 58,769 patients with dementia had an average age of 82 and 63 percent were women. Each dementia case was matched to five control patients of the same age, sex, and general practice. 

Anticholinergic drug exposure was assessed using prescription information over a complete period of 10 years from 1 to 11 years before diagnosis of dementia or the equivalent dates in control patients, and was compared between the two patient groups. Further analysis looked at prescriptions for anticholinergic drugs up to 20 years before diagnosis of dementia.

This is an observational study so no conclusions should be drawn that anticholinergic drugs cause dementia. It is possible that the drugs were being prescribed for very early symptoms of dementia.