A Pilot Study of Terazosin for Parkinson's Disease

Inclusion Criteria: * Men or women aged 40 and older with the diagnosis of idiopathic PD per UK Brain Bank criteria * Hoehn-Yahr Stage I-III, on stable dopaminergic treatment regimen for ≥4 weeks prior to baseline. Exclusion Criteria: * Subjects unwilling or unable to give informed consent * Secondary parkinsonism (e.g., drug induced) * Parkinson-plus syndromes * History of brain surgery for PD such as deep brain stimulation * No confounding acute or unstable medical, psychiatric, orthopedic condition. Subjects who have hypertension, diabetes mellitus, depression, or other common age-related illness will be included if their disease under control with stable treatment regimen for at least 30 days. * Neurogenic orthostatic hypotension defined as symptomatic decrease in BP \> 20mmHg systolic or \> 10mmHg diastolic and HR increase \< 20bpm on supine to sitting or standing. * Clinically significant traumatic brain injury or post-traumatic stress disorder * Presence of other known medical or psychiatric comorbidity that in the investigator's opinion would compromise participation in the study * Presence of dementia per Movement Disorder Society Level I criteria * Major depression, bipolar affective disorder, or other mental health disorders that are sufficiently severe to increase adverse event risk or impact neuropathy assessment in the opinion of the responsible site principal investigator. * Subjects with clinically significant depression as determined by a Beck Depression Inventory score greater than 21 at the screening visit * Current suicidal ideation within one year prior to the baseline visit as evidenced by answering "yes" to Questions 4 or 5 on the suicidal ideation portion of the Columbia-Suicide Severity Rating Scale (C-SSRS) * If the participant has a Beck Anxiety Score greater than 22 at the initial screening visit. * History of exposure to typical or atypical antipsychotics or other dopamine blocking agents within 6 months prior to the baseline visit * Use of investigational drugs within 30 days before screening * Subjects have to be on a stable regimen of central nervous system acting medications (benzodiazepines, antidepressants, hypnotics) for 30 days prior to the baseline visit * Use of doxazosin, alfuzosin, prazosin, or tamsulosin * For female participant, pregnancy, or plans for child-bearing during study period * Participant is restricted from traveling to and from the study site