Additional Study Information: The purpose of this 8-week study is to evaluate the effectiveness of a medication called tianeptine for treating depression in people whose symptoms have not responded to two prior treatments. Tianeptine is an investigational drug. This means that it has not been approved for use by the United States Food and Drug Administration (FDA), the branch of the federal government that approves new drugs, but it has been approved by the European Regulatory Agency and has been used to treat depression in Europe, Asia, and South America since the 1980s.