Systematic review and meta-analysis of intranasal esketamine for treatment-resistant depression in real-world settings

BACKGROUND: Intranasal esketamine has demonstrated efficacy and safety for treatment-resistant depression in randomized controlled trials, however the generalizability of these findings to clinical practice remains unclear. This systematic review and meta-analysis aimed to synthesize real-world evidence of intranasal esketamine in patients with treatment-resistant depression. METHODS: A systematic search was conducted in PubMed, Embase, and PsycINFO up to April 2025 to identify observational studies reporting clinical outcomes of intranasal esketamine in adults with treatment-resistant depression. Standardized mean changes in depressive symptoms and odds ratios for remission were calculated. Random-effects meta-analyses were performed, followed by meta-regression to explore potential moderators. The study protocol was prospectively registered in PROSPERO (CRD420251025075). RESULTS: Nine studies were included in the final synthesis. The analyses demonstrated that intranasal esketamine showed substantial effectiveness, with an effect size of Hedges' g = -1.98 (95% CI -2.94 to -1.03; p < 0.0001). Patients were about five times more likely to achieve remission at three months compared with the induction phase (OR = 5.1, 95% CI 2.29-11.39). Treatment effectiveness was not influenced by factors such as gender or the presence of comorbidities, such as anxiety, personality, or substance use disorders. The pooled prevalence of any adverse event, based on studies that reported safety data, was 82% (95% CI 69-92). The most frequent was dissociation, reported in 49% of patients (95% CI 37-62). CONCLUSIONS: This study provides consistent real-world evidence supporting that Intranasal esketamine was associated with meaningful symptom reduction and rising remission rates over time in real-world settings. Given the observational nature of the evidence and the absence of control groups, effect sizes should be interpreted with caution. Nonetheless, these findings provide valuable insight into esketamine's effectiveness and tolerability in routine practice and highlight the need for controlled comparative studies to guide long-term treatment strategies.