This study investigates the effectiveness of two antipsychotic medications in treating psychosis in individuals with Lewy body disease (LBD), which includes Parkinson's disease (PD) and dementia with Lewy bodies (DLB). The purpose of the study is to compare the improvement in psychosis symptoms between two medications, quetiapine and pimavanserin, over a period of 6 months. Participants will be randomly assigned to one of the two study arms, and their progress will be monitored to determine which medication provides better outcomes.

Participants in the study will undergo routine clinical assessments to evaluate the effectiveness of the assigned medication. These assessments will focus on changes in psychosis symptoms. The study will help provide valuable information on the comparative effectiveness of quetiapine and pimavanserin, guiding future treatment decisions for individuals with LBD.

• Who can participate: Participants must be seen in the neurology clinic at UT Health San Antonio and diagnosed with psychosis due to PD or DLB. They should require the initiation of an antipsychotic medication, with clinical equipoise between quetiapine and pimavanserin.
• Study details: Participants will be randomly assigned to receive either quetiapine or pimavanserin. They will have regular assessments to monitor changes in their psychosis symptoms over the study period. The study will provide insights into the effectiveness of these medications in treating psychosis in LBD.
• Study timelines: The study will last 6 months.