A Donanemab (LY3002813) Study in Participants With Preclinical Alzheimer's Disease (TRAILBLAZER-ALZ 3)

Inclusion Criteria: * A Telephone Interview for Cognitive Status - modified (TICS-M) score reflective of intact cognitive functioning. * Has a phosphorylated tau (P-tau) result consistent with the presence of amyloid pathology. * Has a reliable study partner and backup study partner familiar with overall function and behavior, such as day-to-day activities and cognitive abilities. * Have adequate literacy, vision, and hearing for neuropsychological testing at screening. * Contraceptive use by men or women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies * Female participants include those who are infertile due to surgical sterilization (hysterectomy, bilateral oophorectomy, or tubal ligation), congenital anomaly such as Mullerian agenesis; or post menopausal (women 55 or older not on hormone therapy and had at least 12 months of spontaneous amenorrhea; or with a diagnosis of menopause prior to starting hormone replacement therapy. Treatment Extension: (Study Period II Placebo Group Only) * Are actively participating in Study AACM at the conclusion of Study Period III. Exclusion Criteria: * Mild cognitive impairment or dementia, or significant other neurodegenerative disease that can affect cognition. * Current serious or unstable illnesses including cardiovascular, hepatic, renal, gastroenterologic, respiratory, endocrinologic, neurologic, psychiatric, immunologic, or hematologic disease that c…