A Study of Donanemab (LY3002813) in Participants With Early Symptomatic Alzheimer's Disease

Inclusion Criteria: * Gradual and progressive change in memory function reported by the participant or informant for greater than or equal to (≥) 6 months. * Clinical diagnosis of mild cognitive impairment due to Alzheimer's Disease (AD) or mild Alzheimer's dementia. * Evidence of amyloid pathology confirmed by plasma phosphorylated tau217 (P-tau217) levels. * A Mini Mental State Examination (MMSE) score of 20 to 28 (inclusive). * Have a study partner who will provide written informed consent to participate, is in frequent contact with the participant, and will accompany the participant to study visits or be available by telephone at designated times. Exclusion Criteria: * Have significant neurological disease affecting the central nervous system other than AD. * Have a condition that in the investigator's opinion could interfere with the analyses of this study. * Have a life expectancy of less than 24 months. * Have a presence or history of malignant neoplasms within the past 5 years. * Are actively suicidal. * Have a diagnosis of alcohol or drug use disorder, except tobacco use disorder. * Have a history of clinically significant multiple or severe drug allergies, significant atopy, or severe posttreatment hypersensitivity. * Have previously received or are currently receiving treatment with a passive antiamyloid immunotherapy. * Have received active immunization against amyloid-beta (Aβ) in any other study. * Have known allergies to donanemab, related compounds, or any components of the formulation. * Have any clinically important abnormality at screening. * Screening magnetic resonance imaging (MRI) that shows evidence of significant abnormality that would suggest another potential etiology for progressive dementia or a clinically significant finding that may impact the participant's ability to safely participate in the study. * Have an MRI demonstrating presence of amyloid-related imaging abnormalities that show cerebral edema (ARIA-E), greater than (\>) 4 cerebral microhemorrhages, more than 1 area of cortical superficial siderosis, any macrohemorrhage, or severe white matter disease. * Have any contraindications for MRI, including claustrophobia or the presence of contraindicated metal (ferromagnetic) implants or a cardiac pacemaker. * Poor venous access. * Alanine aminotransferase (ALT) ≥2.5× upper limit of normal (ULN) of the performing laboratory, aspartate aminotransferase (AST) ≥2.5× ULN, total bilirubin (TBL) ≥1.5× ULN, or alkaline phosphatase (ALP) ≥2× ULN at screening.