• Subjects between 40 and 85 years old (inclusive) in good general health:

‣ Willing and able to consent and participate for the duration of the study.

⁃ Have eighth-grade education or good work history sufficient to exclude mental retardation.

⁃ Have visual and auditory acuity adequate for neuropsychological testing.

⁃ Have proficient fluency of the native local language to participate in all the neuropsychological test assessments.

• Have a study partner who has sufficient contact (≥ 2 hours per week) with the subject to assist with dosing of study medication (if necessary) and provide assessments of any changes and an independent evaluation of the subject's functioning.

• Have PDP as defined by all of the following criteria and consistent with the National Institute of Neurological Disorders and Stroke/National Institute of Mental Health (NINDS/NIMH) criteria:

‣ Meets United Kingdom brain bank criteria for PD

⁃ Presence of at least one of the following symptoms

• Illusions

∙ False sense of presence

∙ Hallucinations

∙ Delusions

⁃ The symptoms of Criterion b occur after the onset of PD.

⁃ The symptoms of Criterion b are recurrent or continuous for 1 month.

⁃ The symptoms of Criterion b are not better accounted for by another cause of Parkinsonism such as dementia with Lewy bodies, psychiatric disorders such as schizophrenia, schizoaffective disorder, delusional disorder, or mood disorder with psychotic features, or a general medical condition including delirium.

⁃ May have the following associated features:

• With/without insight

∙ With/without dementia

∙ With/without treatment for PD

• Patients must be experiencing symptom(s) of Criterion 3b at least once a week during the 4 weeks prior to the screening visit.

• Patients being treated for symptom(s) of Criterion 3b must be off medication for at least 2 weeks prior to randomization.

• Patients must be on a stable regimen of medication for PD for at least 4 weeks prior to randomization.

• Permitted medications:

‣ With potential pro-cognitive effects, such as cholinesterase inhibitors, memantine, estrogen replacement therapy, must be at a stable dose for 1 month prior to screening and expected to remain stable throughout the study

⁃ Antidepressants must be at a stable dose for 1 month prior to screening and expected to remain stable throughout the study.

⁃ Antipsychotics must be must be at a stable dose for 1 month prior to screening and expected to remain stable throughout the study.

• Willing and able to undergo repeated MRI scans (3 Tesla) with no contraindications to MRI.

• Participant and partner must both be willing to use an effective contraception for duration of the study and for 4 days after it. For women, effective contraception may be hormonal; for men, a condom.