ObjectiveMajor depression is a significant public health problem since its lifetime prevalence is estimated at 15–18 %. Its standard treatment is based on the use of antidepressant medications but their effectiveness is limited. Indeed, only two thirds of patients with a major depressive episode will reach remission after two lines of conventional treatment. In major depression, there are arguments in favour of disturbances in neuronal glutamatergic transmission. Esketamine appears to have an antidepressant action through modulation of the NMDA receptors involved in this glutamatergic neurotransmission. The aim of this review to systematically investigate the efficacy of esketamine combined with an SSRI or SNRI for major depressive disorder resistant to treatment. MethodA systematic review on the efficacy of esketamine in combination with an SSRI or SNRI for resistant major depressive disorder was performed in July 2021 in the PUBMED database according to the PRISMA criteria. The key words used are: “depressed” [All Fields] OR “depression” [MeSH Terms] OR “depression” [All Fields] OR “depressions” [All Fields] OR “depression s” [All Fields] OR “depressive disorder”[MeSH Terms] OR (“depressive”[All Fields] AND“disorder”[All Fields]) OR“depressive disorder”[All Fields] OR“depressivity”[All Fields] OR“depressive”[All Fields] OR “depressively” [All Fields] OR “depressiveness” [All Fields] OR “depressives” [All Fields]) AND (“esketamine” [Supplementary Concept] OR “esketamine” [All Fields] OR “esketamine” [All Fields]. The inclusion criteria were: efficacy on depressive symptoms of intranasal esketamine combined with an SSRI or an SNRI for major depressive disorder resistant to at least two lines of treatment, RCT and meta-analysis, individual≥18 years, articles in English and French. ResultsFour randomized double-blind studies were selected on the basis of these criteria. The included studies are of grade A and B which leads to a high level of scientific evidence. ConclusionsIntranasal esketamine in combination with sertraline, escitalopram, duloxetine or venlafaxine prolonged release is more effective than the monotherapy use of these four molecules for the treatment of resistant depression. It has been shown to be effective for a population aged between 18 and 74 years at doses between 28mg and 84mg. Currently, based on these results, intranasal esketamine should be proposed as a second level of treatment after an unsuccessful trial of two antidepressants. It is nevertheless advisable to be careful in its use in a clinical psychiatric population: exclusion of suicidal ideation or antecedent of suicidal acting, absence of psychotic depression, use exclusively for unipolar major depressive disorder. The different conditions of use are also notified in the product characteristics of the European Medicines Agency. Finally, further comparative studies are needed in the future, in the absence of funding from the pharmaceutical company producing esketamine.