This is a master protocol for 3 independent, seamlessly enrolling, multicenter, randomized, double-blind, placebo-controlled, parallel-group studies in patients with ADP

• Substudy 1 (Phase 2) will evaluate efficacy and dose response of ACP-204 30 and 60 mg vs placebo. This substudy will be initiated first.
• Substudies 2A and 2B (both: Phase 3) will be confirmatory studies of either both doses (ACP-204 30 and 60 mg, respectively) or a single dose from Part 1 vs placebo. Substudies 2A and 2B will be performed independently of each other and will commence after enrollment of Part 1.

All 3 substudies will be analyzed independently of each other.

Each substudy individually will consist of a screening period (up to 49 days); a double-blind treatment period (6 weeks); a safety follow-up period (30 days) for patients not rolling over into an open-label extension study; and vital status follow-up (for patients who terminated their substudy early).

Inclusion Criteria:

• Is male or female and ≥55 and ≤95 years of age living in the community or in an institutionalized setting
• Meets clinical criteria for possible or probable AD based on the 2011 National Institute on Aging-Alzheimer Association (NIA-AA) criteria
• Meets the revised criteria for psychosis in major or mild neurocognitive disorder established by the International Psychogeriatrics Association (IPA)
• Has either blood-based biomarker or documented evidence (e.g. positron emission tomography, cerebrospinal fluid biomarker) indicating amyloid plaque deposition and neuropathologic change consistent with AD
• Has a prior magnetic resonance imaging or computed tomography scan of the brain that is consistent with the diagnosis of AD
• Meets revised criteria for psychosis in major or mild neurocognitive disorder as per International Psychogeriatrics Association
• MMSE score ≥6 and ≤24
• Psychotic symptoms for at least 2 months
• Lives in a stable place of residence and there are no plans to change living arrangements
• Has a designated study partner/caregiver
• Able to complete all study visits with a study partner/caregiver
• Must be on a stable dose of cholinesterase inhibitor or memantine, if applicable

Exclusion Criteria:

• Requires treatment with a medication prohibited by the protocol
• Is in hospice and receiving end-of-life palliative care, or has become bedridden
• Requires skilled nursing care
• Psychotic symptoms that are primarily attributable to delirium, substance abuse, or a medical or psychiatric condition other than dementia
• Known history of cerebral amyloid angiopathy, epilepsy, central nervous system neoplasm, or unexplained syncope
• Atrial fibrillation
• Symptomatic orthostatic hypotension
• Protocol-defined exclusionary clinical laboratory findings
• Treatment with anti-tau therapy or donanemab within 2 months prior to Screening

Additional inclusion/exclusion criteria apply. Subjects will be evaluated at screening to ensure that all criteria for study participation are met.