My 87 Yr Old Dad Has Been On Aricept For

My 87 yr old Dad has been on Aricept for about 1 yr. He is only able to take a low dose of 10 mg. More than that and he has major side effects. He doesn't like taking it and we don't really know if its doing him any good. What exactly is the drugs action in the body? In simple terminology? He is still highly functional in life even though we see his short term memory getting worse. We just aren't convinced he should be taking this. thank you.