Alzheimer's disease is the most common form of dementia and is the fourth leading cause of death among people 65 years of age and older. The global prevalence of the disease will increase significantly as the population ages, unless preventative treatments can be identified and marketed. The present study seeks to evaluate AZD3480 (TC-1734) compared to an approved medication (donepezil) shown to improve cognition and function in patients with Alzheimer's disease.

This is a double blind, positive comparator, randomized, multicenter, parallel group study to assess the efficacy, safety, and tolerability of AZD3480 as monotherapy in patients with mild to moderate dementia of the Alzheimer's type (AD). Approximately 300 subjects will be randomized and divided into 2 cohorts. Actual randomization was 293 subjects.

Inclusion Criteria:

1. A clinical diagnosis of AD per NINCDS-ADRDA criteria; mild to moderate severity as defined by Mini-Mental State Examination (MMSE) scores of 12 to 22.
2. AD diagnosed at least 12 months prior to Screening, and supported by brain imaging studies within 6 months prior to Screening.
3. Absence of vascular dementia both per AIRENS criteria and as defined by modified Hachinski ischemia score (HIS) of </= 4.
4. Presence of a caregiver with significant proportion of time in contact with subject and who will oversee administration of study drug during the trial
5. Able to complete test assessments and to sign informed consent with the help of a caregiver if needed

Exclusion Criteria:

1. Diagnosis or presence of other dementing illnesses
2. Use of mood stabilizers, antidepressants, anxiolytics, antipsychotics or hypnotics
3. Treatment within 1 month prior to Screening using cognition-affecting agents (e.g. CNS stimulants)
4. Tobacco user within 4 months prior to Screening
5. Use of smoking cessation therapy within 4 months prior to Screening
6. History within past 6 months of alcohol abuse or illicit drug abuse
7. Unable, even with caregiver assistance, to comply with study procedures in opinion of investigator
8. Myocardial infarction within the 12 months prior to Screening
9. Hypothyroidism, vitamin B12 or folic acid deficiency
10. Known systemic infection (HBV, HCV, HIV, TB)
11. Vascular dementia per NINDS-AIRENS criteria and as defined by a modified Hachinski ischemia score (HIS, Appendix 4) score of > 4 (i.e., vascular dementia is consistent with a modified HIS > 4).