Concurrent Use of Anticholinergic and Antidementia Medicines in Older Adults with Dementia: A Systematic Review of Prevalence, Predictors and Clinical Outcomes.

Background: Concurrent use of acetylcholinesterase inhibitors (AChEIs) and medicines with anticholinergic activity is a clinically important medication safety concern in dementia care because these medicines may pharmacologically oppose dementia treatment and increase the risk of avoidable harm. This review systematically synthesised evidence on the prevalence, patterns, predictors and clinical consequences of concurrent use of anticholinergic and anti-dementia drugs (ADDs) in older adults with dementia. Methods: A PRISMA-informed systematic review was conducted employing Ovid MEDLINE, Embase and PsycINFO from January 2010 to April 2026. Observational studies were eligible if they included older adults with dementia and reported concurrent exposure to at least one anticholinergic medicine and an ADD, defined as AChEIs and/or memantine. Study quality was appraised using the Newcastle-Ottawa Scale. Results: Twenty-eight studies were included, spanning community, outpatient memory-clinic, acute hospital, long-term care and population-based settings. Two distinct exposure constructs were identified: (1) temporal co-prescribing and (2) cumulative anticholinergic burden among ADD users. Reported prevalence varied markedly according to the exposure definition and setting. Concurrent use was lowest in studies limited to bladder antimuscarinic overlap, generally around 5-13%,but increased to 20-45% when broader anticholinergic definitions were used. In long-term care and institutional cohorts, concurrent exposure reached 61-67%. Recurring predictors included polypharmacy, fragmented care or multiple prescribers, urinary symptoms, behavioural and psychological symptoms of dementia, Parkinson's disease and non-geriatric prescribing. One large population-based study reported that high anticholinergic burden was associated with treatment modification of AChEIs (aHR 1.12), delirium (aHR 1.52), and two-year mortality (aHR 1.23). Additional studies reported associations with longer hospital stays or readmission. Conclusions: Concurrent use of anticholinergic medicines and ADDs is a common, clinically important and potentially modifiable medication-safety problem in dementia care.