Light and Ion Maintenance In Treatment for Depression (LIMIT-D): Feasibility Study

Inclusion Criteria: * Diagnostic and Statistical Manual (DSM-5) criteria for MDD, as determined by the Structured Clinical Interview for DSM-5 (SCID). * Taking a first-line antidepressant at approved doses (Table 1), with dose unchanged in the past month. * Participant desire to discontinue antidepressant treatment because of adverse effects or other reasons; * In remission as defined by score ≤10 on the clinician-rated Montgomery-Asberg Depression Rating Scale (MADRS) at both the screening visit and baseline visit, at least 2 weeks apart. * Willing and able to complete self-report and online assessments including sufficient fluency in English or French. Exclusion Criteria: * Any psychiatric diagnosis other than MDD that is considered the primary diagnosis, including Bipolar I or Bipolar-II (lifetime). Note that comorbid anxiety disorders (e.g., generalized anxiety disorder, social anxiety disorder) will not be excluded if the anxiety disorder is not the primary diagnosis. * Diagnosis of MDD with seasonal pattern (i.e., seasonal affective disorder, SAD) or with psychotic features (lifetime). * Significant personality disorder diagnosis \[e.g., antisocial\] by MINI and clinical assessment. * High suicidal risk, defined by clinician judgment. * History of alcohol or substance use disorder, with a severity of at least moderate or severe, within 6 months before screening. * Significant neurological disorders, head trauma, or other unstable medical conditions. * Regular use of psychotropic medication other than an antidepressant or benzodiazepines (e.g., antipsychotics, mood stabilizers); Note - Stimulant medications for Attention-Deficit Hyperactivity Disorder are allowed if dose is stable in past month. * History of severe antidepressant discontinuation effects. * Retinal disease or other eye condition (e.g., macular degeneration) precluding the use of bright light treatment. * Use of photosensitizing medication (thioridazine, chloroquine, 8-methoxypsoralen) within 1 week of baseline visit. * Initiated formal psychotherapy (e.g., cognitive-behavioural therapy) within 3 months of Visit 1, or who plan to initiate psychotherapy during the study. * Continued use of any other evidence-based treatment for depression.