Measuring Psychomotor Response to L-DOPA Challenge As a Biomarker for Outcomes in Late-Life Depression: a Pilot Feasibility Trial

Inclusion Criteria: * Outpatient persons capable of providing informed consent * Minimum age of 60 years old * MINI International Neuropsychiatric Interview diagnosis of major depressive disorder, based on DSM-5 criteria * MADRS score of ≥15 (moderate/severe depression) * On stable doses of psychotropic medication, including antidepressant medication, for at least 4 weeks * Able to adhere to the intervention schedule Exclusion Criteria: * Current diagnosis of major neurocognitive disorder * Current active psychosis * Unstable medical illness, including clinical or laboratory evidence of uncompensated cardiovascular, endocrine, hematologic, hepatic, pulmonary (including bronchial asthma), or renal disease * Diagnosis of narrow angle glaucoma * Suspicious, undiagnosed skin lesions or a history of melanoma * History of myocardial infarction * Atrial, nodal, or ventricular arrhythmias * History of seizures or seizure disorder * History of peptic ulcer disease * History of allergy or other hypersensitivity to levodopa, carbidopa, or to any other ingredient in the formulation of Levocarb * Active suicidal ideation * Psychotropic medication initiation or dose change \<4 weeks prior to enrolment * Regular use of dopamine antagonist or benzodiazepines ≥2mg lorazepam equivalent per day * Unable to complete neuropsychological testing in the English language * Have a non-correctable clinically significant sensory impairment (i.e., cannot hear or see well enough to complete the neuropsychological tests) * History of falls, with ≥1 fall per week during the past 4 weeks