Citalopram as a Posterior Cortical Protective Therapy in Parkinson Disease

Inclusion Criteria: * Subjects with a Parkinson Disease (PD) diagnosis based on the United Kingdom Parkinson's Disease Society Brain Bank Research Center clinical diagnostic criteria * Modified Hoehn and Yahr (HY) scores spanning 2.0 to 3.0 * Age 65 years or greater Exclusion Criteria: * Diagnosis of an atypical parkinsonian condition * Participants on neuroleptics and participants with a history of use of anti-depressants (including selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), bupropion, St. John's Wort or other serotoninergic agents in the year preceding study enrollment * Evidence of a large artery stroke or mass lesion on brain imaging * Participants with a life threatening comorbid illness * Severe claustrophobia precluding PET imaging * Inability to participate in research procedures involving ionizing radiation * Pregnancy or breastfeeding * Participants with active depression as defined by a Geriatric Depression Scale score of \>10 or on the basis of clinical diagnosis by the PI * Participants who report active suicidal ideation as defined by an affirmative answer to questions 1 and 2 on the C-SSRS * Participants with baseline HY scores \<2.0 or ≥3.0 * Participants with a QTc interval on baseline EKG \>0.45 for men or \>0.47 for women * Subjects taking certain contraindicated medications at baseline * Subjects unable to swallow pills * Subjects with a previous history of mania, ongoing hepatic impairment or epilepsy * Subjects with a known allergy to citalopram or escitalopram * Subjects with substantial cognitive impairment or dementia that would prevent them from providing informed consent * Subjects in another ongoing clinical trial * Subjects with treatment-naieve Parkinson disease