Mood Stabilizer (MS)+ Antidepressant vs MS + Placebo in Maintenance of Bipolar Disorder.

Study Design: The investigators propose a multicentre, randomized, double-blind, placebo-controlled trial in patients with BD who are currently experiencing a depressive episode. The trial will consist of two phases: an open-label acute treatment phase, and a double-blind maintenance treatment phase. OPEN-LABEL ACUTE TREATMENT PHASE Experimental Design Patients with BD depression who are receiving treatment with antimanic medication(s), defined as: 1) a mood stabilizer (lithium or divalproex ), 2) a second-generation antipsychotic (SGA) (risperidone, olanzapine, quetiapine, aripiprazole, or ziprasidone), or 3) combination anti-manic therapy (two mood stabilizers; or a mood stabilizer plus an SGA (the SGA asenapine will also be permitted if prescribed with a mood stabilizer); or a mood stabilizer or SGA plus lamotrigine), will have open-label escitalopram 10-30 mg/day or bupropion XL 150-450 mg/day added to their medication(s) for up to 16 weeks.Patients who complete at least 4 weeks of treatment and achieve remission from their index depression which is maintained for ≥ 2 weeks will be eligible to enter the double-blind study phase. The duration of treatment in the open-label phase will be 4-16 weeks, depending on the time required to achieve remission. DOUBLE-BLIND MAINTENANCE TREATMENT PHASE Patients who are in remission from their index depression for ≥ 2 weeks and ≤ 8 weeks are eligible to take part in the double-blind maintenance phase. There are two routes to enter the double-blind phase: * following completion of the open-label phase, or * following a period of clinical treatment, not exceeding 16 weeks, with the same medications used in the open-label phase. Patients who respond to clinical treatment with carbamazepine plus an antidepressant may also enter the double-blind phase. Experimental Design During the double-blind phase, all patients will continue treatment with their anti-manic medication(s) and will be randomized to one of two treatment arms for up to 52 weeks: * Patients randomized to the "8 week arm" will discontinue antidepressant treatment after 8 weeks, as recommended in current clinical practice guidelines.. * Patients randomized to the "52 week arm" will continue treatment with their antidepressant medication for 52 weeks, or until withdrawal from the study.