[Unsatisfactory response: definition and involvement]

In the treatment of unipolar depression, treatment response is a key issue in terms of evolution and prognosis. Within this concept, the inadequate response includes the worsening, the lack of response, partial response and poor tolerance. This lack of response may be related to intrinsic factors to the individual, but also to more extrinsic environmental factors. In this review, we explore this concept through its links with adherence and treatment duration. In this field, the concept of early response can be a powerful indicator of therapeutic response, which conditions the prescription of antidepressants beyond the strict framework of the sufficient period of 4 to 6 weeks. In addition to its impact on prognosis, the literature data show that the insufficient response is a significant burden in terms of medical and economic cost, and somatic comorbidity; and justifies a systematic identification of this dimension. Therefore self-reports (QIDS; BDI) will be preferred to the clinician-rated depression symptom rating scales (MADRS, HAMD) that require a specific training. Identifying predictors of non-response would be an attractive target for prescribers but the results to date are not operative.