While there is evidence to support the efficacy of switch and add-on strategies, information on how these strategies should be sequenced is lacking. Most switch and add-on studies have focused on treatment-resistant depression defined as treatment failure (i.e., a d20% reduction in depression scores) after t2 antidepressant trials. Little information is available for effective therapy for partial response (20–49% reduction in depressive symptoms) or for residual symptoms (>50% reduction) (Lam et al., 2009). See Figure 1.