Why do people with dementia have a greater risk of developing an adverse reaction to anticholinergics?

Acetylcholine. Anticholinergic medications block the effect of acetylcholine, a brain chemical that plays a key role in the process of remembering. Mental status changes associated with anticholinergics can range from mild cognitive impairment to delirium. Patients with alzheimer's disease and other dementias are especially sensitive due to already existing cholinergic abnormalities.
Anticholinergics. Further decrease acetylcholine, which is one of the neurotransmitters involved in memory.