Safety and Efficacy of Donepezil HCl 23 mg in Patients With Moderate to Severe Alzheimer's Disease

1. Male or female aged 45 to 90 years

2. Patients have eligible conditions of dementia diagnosis listed in DSM-IV

3. Diagnosed as a probable Alzheimer's Disease patient according to NINCDS-ADRDA criteria

4. At the timing of screening, MMSE less than or equal to 20 AND CDR greater than or equal to 2 OR GDS greater than or equal to 4

5. Patients, who have been taking stable donepezil 10 mg for 3 months or longer before the start of the study (screening visit), are evaluated as eligible to take donepezil 23 mg by investigator

6. Patients who have not received any other medications for AD such as AChE inhibitors at least for 3 months prior to the screening visit excluding donepezil hydrochloride (However, concomitant use of memantine is allowed if taken at stable dose that are less than or equal to the approved dose range for at least 3 months prior to screening)

7. Medicines for cerebral activation such as Gingko Biloba is allowed to be taken if the patient has received it as stable dose for 3 months prior to the screening visit

1. Patients who have been participated in any other clinical trial 3 months prior to the screening visit

2. Patients who are having any severe psychiatric disorder or schizophrenia

3. Patients who are having a neurological disorder other than AD which affect the subject's cognition or ability to assess the cognition