What could happen if i take my dad (89 yrs old) off aricept (donepezil) after being on it for 6 yrs., if he really does have dementia?

Aricept (donepezil): Helps reduce the symptoms of dementia. Stopping it may increase those symptoms. Discuss with his neurologist before making any changes.

New behaviors: Three things are possible: no change, a rapid (over weeks) decline in functioning that he cannot regain even if medicine restarted or more likely the emergence of previously unseen behavioral problems. The medicines like Aricept (donepezil) decrease anxiety and agitation and have a protective effect against hallucinations and delusions.

Maybe very little: Research studies suggest that Aricept is of limited value after about 2 or 3 yrs in most pts, and might be no noticeable effect when stopped. In some, there is a precipitous deterioration over 6 weeks, and there is no way of predicting which way this will go. Maybe, substitute an Exelon (rivastigmine) patch if you are concerned.