Inclusion Criteria:

1. Male or post menopausal female patients aged ≧50 years old;
2. The informed consent must be signed by the patient and co-signed by their proxy or principal caregivers before undergoing any study procedures;
3. Probable Alzheimer’s disease based on the National Institute of Neurological and Communicative Disorders and Alzheimer’s dementia and related disorder (NINCDS-ADRDA)
4. Patients with Mini-Mental State Examination (MMSE) scores of 12~24
5. Patients with Clinical Dementia Rating (CDR)in mild (CDR = 1) and moderate (CDR = 2) AD
6. Cranial computed tomography (CT) or brain magnetic resonance imaging (MRI) must be within the past 12 months;
7. Patients must be able to complete baseline assessments;
8. An eligible principal caregiver must be able to accompany the patient to all scheduled visits;
9. Patients currently taking ChEIs such as donepezil, rivastigmine, or galantamine are allowed if the dose has been unchanged for the last 3 months before the study entry.

Exclusion Criteria:

1. Patients with history of severe systemic disease such as coronary artery disease, myocardial infarct, progressive heart failure, chronic obstructive pulmonary disease within the past 1 year;
2. Patients with hepatic and renal insufficiency (ALT、AST 3 times above normal range; serum creatinine 2 times above normal range), diabetic patients with poor control of blood sugar (HbA1c＞8.5) at study entry;
3. Patients with central nervous system disease other than AD such as cerebral vascular disease, Parkinson’s disease, epilepsy, traumatic brain injury, central nervous system infection, and alcoholic encephalopathy;
4. Patients with concurrent psychosis or mood disorder (Hamilton depression scale score > 17);
5. Patients diagnosed cancer and treated within the past two years (except for non-invasive skin cancer);
6. Patients with general medical conditions, which may confound the results of the study, pose additional risk or preclude evaluation and assessments in this study as judged by the investigator;
7. Patients currently treated with any prohibited medications (listed in Concomitant Treatment section) are not able to fulfill the 2 week-washout period;
8. Participation in another study within the last 30 days;
9. Females who are within two years of their menopause unless proved not pregnant (determined by urine test);
10. Dementia caused by other etiology as indicated by clinically significant abnormal Vit B12, folic acid, or thyroid function tests.
11. Patients with neurosyphilis confirmed by CSF STS/TPHA;
12. The neuroimage CT or MRI could not be compatible with the diagnosis of probable AD as stated in the NINCDS criteria;
13. Patients with a Hachinski score (Appendix 5) above 3 are excluded.