• The patient must be diagnosed with non-psychotic unipolar Major Depressive Disorder.

• The patient must be in a major depressive episode for ≥12 months or have had at least 3 lifetime depressive episodes.

• The patient has tried and failed a minimum of four different types of antidepressant treatments as measured by a tool designed for this purpose.

• Depression medication and treatment regimen must be stable for a minimum of 4 weeks before the first baseline visit