Systematic Review of Second-Generation Antidepressant Monotherapy for Acute Bipolar-II Depression.

Purpose: Individuals with Bipolar II disorder (BD-II) face high rates of depression and have limited FDA-approved treatments, leading to treatment delays and poor functioning. Although not commonly recommended, monoaminergic antidepressants are prescribed to 50% of patients. This review updates the evidence for second-generation antidepressant (SGAD) monotherapy in treating acute BD-II depression. Methods: We searched Ovid MEDLINE, Embase, CENTRAL, PsycINFO, Scopus, and Web of Science from March 2021 to February 2025 and included five studies published before 2021. Randomized controlled trials (RCTs) evaluating SGAD monotherapy in adults with acute BD-II depression. Primary outcomes were response, remission, treatment-emergent affective switch (TEAS), dropouts owing to adverse events (AEs), and overall discontinuations. Results: Of 949 records identified, 12 studies were selected for full-text assessment, and six were included in our systematic review. The final dataset comprised four double-blind RCTs (n = 533), one open-label RCT (n = 83), and one triple-blind RCT (n = 40). Venlafaxine and sertraline produced short-term benefits, with response rates 60.4%-73.3% and remission rates 44.2%-58.5%. TEAS risk was ⩽ 19.9% and did not differ from lithium in head-to-head comparisons. AEs withdrawals were similar; SGADs often had comparable or better all-cause discontinuation than comparators. Conclusions: Limited short-term evidence indicates that SGAD monotherapy in acute BD-II depression is well-tolerated and has similar response rates to lithium, without increasing switch risk. Nevertheless, the evidence base is small and heterogeneous. Larger and longer RCTs are needed to confirm efficacy, characterize maintenance benefits, and inform personalized treatment decisions.