 This is an enriched maintenance study of the use of tianeptine as an adjunctive therapy in bipolar depression. All participants will receive tianeptine in an open label manner for a period of two months, following which they will be assigned randomly to the treatment with tianeptine or placebo in a double-blind fashion for six months. All patients will remain on treatment as usual for the duration of the trial. Along with clinical response, the investigators will prospectively evaluate the improvement in working and declarative memory, two cognitive prefrontal- and hippocampus-dependent processes, respectively, and the effects of tianeptine on serum BDNF levels. 