What the studies found
It’s important to note that neither of these studies was a randomized controlled clinical trial, so neither proved that either type of drug causes dementia.
The anticholinergic study.
Researchers tracked nearly 3,500 men and women ages 65 or older who took part in Adult Changes in Thought (ACT), a long-term study conducted by the University of Washington and Group Health, a Seattle health care system. They used Group Health’s pharmacy records to determine all the drugs, both prescription and over-the-counter, that each participant took in the 10 years before starting the study. Participants’ health was tracked for an average of seven years. During that time, 800 of them developed dementia. When the researchers examined medication use, they found that people who used anticholinergic drugs were more likely to have developed dementia than those who didn’t use them. Moreover, dementia risk increased along with the cumulative dose. Taking an anticholinergic for the equivalent of three years or more was associated with a 54% higher dementia risk than taking the same dose for three months or less.
The University of Washington study is the first to include nonprescription drugs. It is also the first to eliminate the possibility that people were taking the drugs to alleviate early symptoms of undiagnosed dementia. For people who took anticholinergic bladder medications, the increased risk was just as high as for those taking tricyclic antidepressants, which are also anticholinergics.