Intervention: Quetiapine
Trial phase: Phase 2
ATC code: N05AH04
SMILES: OCCOCCN1CCN(C2=Nc3ccccc3Sc3ccccc32)CC1
Sex: All
Age groups: Adult | Older Adult
Healthy volunteers: No
Participants at risk: 4
Group description: Quetiapine starting dose 25 mg once daily (provided as 1 × 25 mg quetiapine immediate release encapsulated tablet plus 1 placebo encapsulated tablet), with the possibility to increase the dose to 50 mg (2 × 25 mg quetiapine immediate release encapsulated tablets) or 100 mg (2 × 50 mg quetiapine immediate release encapsulated tablets) taken once daily, based on clinical response.
Eligibility criteria:
Inclusion Criteria:

Male or female subjects 50 to 85 years of age, inclusive
Able to understand the protocol requirements and provide written informed consent
Able to complete questions on a handheld device / tablet, is willing to wear an actigraph and can be reliably rated on assessment scales
Able to designate an 'informant' (relative, housemate, friend) who can provide information about the subject's well being and attend clinic visits with the subject
Is able to swallow the test capsule without difficulty during the Screening visit
Has a Mini-Mental State Examination (MMSE) score ≥19
Has a diagnosis of idiopathic Parkinson's disease, without any other known or suspected cause of parkinsonism. Initial diagnosis of PD must have been made more than 1 year prior to Screening.
Has non-motor neuropsychiatric symptoms severe enough to warrant treatment with an antipsychotic agent based on investigator judgement and CGI-S score
If the subject is on anti-Parkinsonian medication, they must be on a stable regimen for 1 month prior to Baseline and not planning (at the time of the Baseline visit) to make a major change in dose(s)
If the subject is female, she must not be pregnant or breastfeeding. She must also be of non-childbearing potential or must agree to use a clinically acceptable method of contraception or be abstinent for at least 1 month prior to the Baseline visit, during the study, and 41 days following completion of double-blind treatment.

Exclusion Criteria:

Has atypical parkinsonism or secondary parkinsonism variants such as tardive or medication induced parkinsonism
Is in hospice, is receiving end-of-life palliative care, or is bedridden or confined to a wheelchair
Has neuropsychiatric symptoms that are primarily attributable to current delirium or substance abuse
Has current evidence of an unstable neurological, cardiovascular, respiratory, gastrointestinal, renal, hepatic, hematologic, or other medical or psychiatric disorder, including cancer or malignancies that, in the judgment of the Investigator, would jeopardize the safe participation of the subject in the study or significantly interfere with the conduct or interpretation of the study
Has a known personal or family history of long QT syndrome or family history of sudden cardiac death
Has orthostatic hypotension as judged by the investigator and medical monitor
Is judged by the Investigator or the Medical Monitor to be inappropriate for the study for any reason, including if the subject is judged to be a danger to self or others

Additional inclusion/exclusion criteria apply. Patients will be evaluated at screening to ensure that all criteria for study participation are met. Patients may be excluded from the study based on these assessments (and specifically, if it is determined that their baseline health and condition do not meet all pre-specified entry criteria).