Relapse Prevention Study of Pimavanserin in Dementia-related Psychosis

Inclusion Criteria:

1. Meets criteria for All-cause Dementia according to NIA-AA guidelines
2. Meets clinical criteria for one of the following disorders: Dementia associated withParkinson's disease, Dementia with Lewy bodies, Possible or probable Alzheimer'sdisease, Frontotemporal degeneration spectrum disorders, Vascular dementia
3. Has an MMSE score ≥6 and ≤24
4. Has had psychotic symptoms for at least 2 months
5. Must be on a stable does of cholinesterase inhibitor or memantine, if applicable
6. If the subject is female, she must not be pregnant or breastfeeding. She must also beof non-childbearing potential or must agree to use a clinically acceptable method ofcontraception for the duration of the study

Exclusion Criteria:

1. Has psychotic symptoms that are primarily attributable to a condition other thandementia
2. Has had a recent major depressive episode
3. Has experienced suicidal ideation or behavior within 3 months prior to studyenrollment
4. Has evidence of a non-neurologic medical comorbidity or medication use that couldsubstantially impair cognition
5. Has a history of ischemic stroke within the last 12 months or any evidence ofhemorrhagic stroke
6. Has a known history of cerebral amyloid angiopathy (CAA), epilepsy, CNS neoplasm, orunexplained syncope
7. Has any of the following: greater than New York Heart Association (NYHA) Class 2congestive heart failure, Grade 2 or greater angina pectoris, sustained ventriculartachycardia, ventricular fibrillation, torsade de pointes, syncope due to anarrhythmia, an implantable cardiac defibrillator
8. Had a myocardial infarction within the last 6 months
9. Has a known personal or family history or symptoms of long QT syndrome
10. Has a significant unstable medical condition that could interfere with subject'sability to complete the study or comply with study procedures
11. Requires treatment with a medication or other substance that is prohibited by theprotocol Additional inclusion/exclusion criteria apply. Subjects will be evaluated at screening toensure that all criteria for study participation are met.