Evaluation of antidepressant polypharmacy and other interventions for treatment-resistant depression

There is on-going controversy about the definition and sub-classification of treatment-resistant depression (TRD) that makes it difficult to assess the effectiveness of different proposed strategies for treating this chronic, often disabling condition. Sub-classification of TRD in terms of symptom severity and in terms of demographic and clinical characteristics may help in the recognition of homogeneous TRD subgroups and in the development of subgroup-specific interventions.