The purpose of this Phase III study is to evaluate the efficacy and safety of 3APS compared to placebo (inactive substance pill) in patients with mild to moderate Alzheimer's disease.
Inclusion Criteria: Patients may be included in this study if they meet all of the following criteria: * Male or Female (age 50 years and older): Female must be of non-childbearing potential (i.e. surgically sterilized or at least 2 years post-menopausal). * Diagnosis of probable Alzheimer's disease based on the National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA criteria). * Severity of dementia of mild to moderate degree as assessed by the Mini Mental State Examination (MMSE) performed at the screening visit. * Patient must be living in the community with a reliable caregiver. Participant living in an assisted living facility may be included if study medication intake is supervised and participant has a reliable caregiver. * Potential participant must be treated with conventional Alzheimer's disease therapies and must be on stable dose for at least 4 months prior to the screening visit and during the entire study period. * Fluency in English, French or Spanish (oral and written). * Signed informed consent from potential participant or legal representative and caregiver. Exclusion Criteria: Patients will not be eligible to participate in the study if they meet any of the following criteria: * Potential participant with any other cause of dementia. * Life expectancy less than 2 years. * Potential participant with a clinically significant and/or uncontrolled condition or other significant medical disease. * Use of an investigational drug within 30 days prior to the screening visit or during the entire study. * Previous use of 3APS. Patient recruitment is done by participating centers.