Abstract
The most largely used definition of the treatment-resistant depression relies on the failure of two successive trials of antidepressant treatment at an adequate dose and duration. The absence of response to previous antidepressant treatments should be assessed using specific and appropriate clinical instruments enabling a correct staging of the therapeutic resistance. A wide range of socio-demographic and clinical factors (i.e. psychiatric/somatic comorbidities) are classically associated with the therapeutic resistance. The aim of the treatment of major depression is to achieve a complete clinical remission. The presence of residual symptoms increases the risk for the subsequent occurrence of relapses and recurrences, hence facilitating the development of therapeutic resistance. The treatment-resistant depression has a deleterious impact on the social, familial or professional functioning, thereby leading to an impaired quality of life with serious socioeconomic consequences and costs.