[French Society for Biological Psychiatry and Neuropsychopharmacology and Fondation FondaMental task force: Formal Consensus for the management of treatment-resistant depression].

Major depression represents among the most frequent psychiatric disorders in the general population with an estimated lifetime prevalence of 16-17%. It is characterized by high levels of comorbidities with other psychiatric conditions or somatic diseases as well as a recurrent or chronic course in 50 to 80% of the cases leading to negative repercussions on the daily functioning, with an impaired quality of life, and to severe direct/indirect costs. Large cohort studies have supported that failure of a first-line antidepressant treatment is observed in more than 60% of patients. In this case, several treatment strategies have been proposed by classical evidence-based guidelines from internationally recognized scientific societies, referring primarily on: I) the switch to another antidepressant of the same or different class; II) the combination with another antidepressant of complementary pharmacological profile; III) the addition of a wide range of pharmacological agents intending to potentiate the therapeutic effects of the ongoing antidepressant medication; IV) the association with appropriate psychological therapies; and, V) the use of non-invasive brain stimulation techniques. However, although based on the most recently available data and rigorous methodology, standard guidelines have the significant disadvantage of not covering a large variety of clinical conditions, while currently observed in everyday clinical practice. From these considerations, formalized recommendations by a large panel of French experts in the management of depressed patients have been developed under the shared sponsorship of the French Association of Biological Psychiatry and Neuropsychopharmacology (AFPBN) and the Fondation FondaMental. These French recommendations are presented in this special issue in order to provide relevant information about the treatment choices to make, depending particularly on the clinical response to previous treatment lines or the complexity of clinical situations (clinical features, specific populations, psychiatric comorbidities, etc.). Thus, the present approach will be especially helpful for the clinicians enabling to substantially facilitate and guide their clinical decision when confronted to difficult-to-treat forms of major depression in the daily clinical practice. This will be expected to significantly improve the poor prognosis of the treatment-resistant depression thereby lowering the clinical, functional and costly impact owing directly to the disease.