Open Label Study of ATH-1017 for Treatment of Mild to Moderate Alzheimer's Disease

Inclusion Criteria: * Subject has completed the Week 26 visit of either of the two blinded parent studies (ATH-1017-AD-0201 or ATH-1017-AD-0202). * Reliable and capable support person/caregiver who is willing to accept responsibility for supervising the daily treatment or, if required, administering study drug. * Subject capable of giving signed informed consent, or by a legally acceptable representative. * Subjects must be in generally good health. * Male subjects and their partners must agree to continue to use a double-barrier method of contraception during the study, including the follow-up period, unless the partner is not of childbearing potential. Exclusion Criteria: * Subject has experienced a serious adverse event during the parent study, which could present an increased safety risk during the open label extension. * New diagnosis of severe major depressive disorder even without psychotic features. * Any subject with formalized delusions or hallucinations. * Significant suicide risk. * Newly-diagnosed malignant tumor, except for the following conditions that are stable in the judgement of the investigator: * Adequately treated squamous and basal cell carcinoma, or squamous and basal cell carcinoma in situ * Prostate carcinoma in situ