Like the other cholinesterase inhibitors, recent studies indicate that Exelon may be effective, at least in some patients, for at least five years.

Rivastigmine in Alzheimer's disease: Cognitive function and quality of life
Rivastigmine in Alzheimer's disease: Cognitive function and quality of life. Annicchiarico R, Federici A, Pettenati C, Caltagirone C. Correspondence: Roberta Annicchiarico I.R.C.C.S. Fondazione
http://www.pubmedcentral.nih.gov/articlerender.fcg...