Final answer:
The major side effect of benztropine is delirium, which occurs because it is an anticholinergic drug that can cross the blood-brain barrier and affect the central nervous system.
Step-by-step explanation:
The major side effect of benztropine is delirium. Benztropine is an anticholinergic drug used primarily in the treatment of Parkinson's disease and extrapyramidal symptoms. It works by blocking acetylcholine receptors, which can lead to a reduction in muscle stiffness and tremors. However, as with many anticholinergic drugs, benztropine can cross the blood-brain barrier and affect the central nervous system, potentially causing side effects such as confusion, disorientation, and delirium, especially in the elderly or those with pre-existing cognitive impairments.