A large study, involving 3,690 older adults, has found that drugs with strong anticholinergic effects cause memory and cognitive impairment when taken continuously for a mere two months. Moreover, taking multiple drugs with weaker anticholinergic effects, such as many common over-the-counter digestive aids, affected cognition after 90 days’ continuous use. In both these cases, the risk of cognitive impairment doubled (approximately).
More positively, risk of Alzheimer’s did not seem to be affected (however, I do have to wonder how much weight we can put on that, given the apparent length of the study — although this is not a journal to which I have access, so I can’t be sure of that).
Although somewhat unexpected, previous research linking anticholinergics and cognitive impairment is consistent with this new finding.
Anticholinergic drugs block the neurotransmitter acetylcholine. Older adults commonly use over-the-counter drugs with anticholinergic effects as sleep aids and to relieve bladder leakage. Drugs with anticholinergic effects are also frequently prescribed for many chronic diseases including hypertension, cardiovascular disease and chronic obstructive pulmonary disease.
You can download a list detailing the ‘anticholinergic burden’ of medications at: http://www.indydiscoverynetwork.org/AnticholinergicCognitiveBurdenScale.html
 Long-term anticholinergic use and the aging brain. Alzheimer's & Dementia: The Journal of the Alzheimer's Association. 9(4), 377 - 385.(2013).