A Study to Evaluate the Efficacy, Safety and Tolerability of SEP-363856 in Subjects With Parkinson's Disease Psychosis

Inclusion Criteria: * Subject, caregiver, and/or legally authorized representative understands and is willing to sign informed consent to participate in the study. * Subject must be willing and able to comply with the study procedures and visit schedules and must be able to follow verbal and written instructions. * Subject is male or postmenopausal female ≥ 55 years of age. * Subject meets established diagnostic criteria for Parkinson's disease of at least one year duration, consistent with the UK Brain Bank criteria * Subject has psychotic symptoms that began after the diagnosis of PD for at least one month, occurring at least weekly in the month prior to screening (according to subject or caregiver), and severe enough to warrant treatment with antipsychotics. * Subject has a combined score of at least 6 or an individual score of at least 4 on the neuropsychiatric inventory (NPI) Item A (delusions) and/or Item B (hallucinations). This crieterion must be met at Visit 1 and Visit 3. * Subject has a Mini-mental status examination (MMSE) score \> 21 points out of 30. * Subject has a caregiver (spouse or family member) who will be required to attend all visits and is able to provide study information on various scales such as the NPI. * Subject is taking antiparkinsonian drugs or deep brain stimulation, with a stable dose/dose regimen and settings for 3 months before enrolment. * Female subject must be postmenopausal defined as being amenorrheic for greater than two years with a…