Aricept (donepezil) has been approved by the FDA for treating all stages of Alzheimer's -- mild, moderate, and severe. It can take up to 3 weeks for any positive effects to appear. Recent studies show that it may be helpful for several years, especially in combination with Namenda (memantine); and may delay or prevent the development of serious behavioral symptoms.

Aricept (donepezil) approved for all stages of Alzheimer's
INDICATIONS ARICEPT® is indicated for the treatment of dementia of the Alzheimer's type. Efficacy has been demonstrated in patients with mild to moderate Alzheimer's Disease, as well as in patients
http://www.rxlist.com/aricept-drug.htm
Aricept (donepezil) for Severe Alzheimer's
3 April 2006. With the exception of the glutamate antagonist memantine, the only drug treatments currently approved by the U.S. Food and Drug Administration for treating Alzheimer disease are cholines
http://www.alzforum.org/new/detail.asp...