Study has been suspended due to clinical hold.

This is a 26-week, randomized extension of the Phase 3 double-blind placebo-controlled studies, EVP-6124-024 and EVP-6124-025. In this extension study, subjects who complete study EVP-6124-024 or EVP-6124-025 and fulfill all entry criteria will be randomized to receive EVP-6124 for an additional 26 weeks.

Inclusion Criteria:

• Male or female subjects of any race, aged ≥55 and ≤85 years at time of entry into study EVP-6124-024 or EVP-6124-025
• Informed consent form (ICF) for this extension study signed by the subject or legally acceptable representative and an ICF signed by the support person/caregiver before initiation of any study-specific procedures
• Successful completion (Day 182) of study EVP-6124-024 or EVP-6124-025
• No clinically significant change in the judgment of the investigator in the subject's medical status during study EVP-6124-024 or EVP-6124-025
• In the judgment of the investigator, extension treatment is in the best interest of the subject
• Fertile, sexually active subjects (men and women) must use an effective method of contraception during the study. Female subjects and the female partner of male subjects must be surgically sterile (hysterectomy or bilateral tubal ligation), postmenopausal for at least 1-year, or willing to practice adequate methods of contraception if of childbearing potential (defined as consistent use of combined effective methods of contraception [including at least 1 barrier method])
• Reliable and capable support person/caregiver, who if not living in the same household, interacts with the subject approximately 4 times per week and will be available to attend clinic visits in person when possible

Exclusion Criteria:

• Significant risk of suicidal or violent behavior in the judgment of the investigator
• Adverse events from the previous study (EVP-6124-024 or EVP-6124-025) that have not resolved, are moderate or severe, judged to be possibly related or related to study drug, and considered by the investigator to be a contraindication to extension study participation
• Any condition that would make the subject in the judgment of the investigator unsuitable for the study
• Female subjects who are pregnant, nursing, or planning to become pregnant during the extension study