Essential oil-based interventions for chemotherapy-induced nausea and vomiting in women with breast cancer: a systematic review and meta-analysis.

OBJECTIVES: Chemotherapy-induced nausea and vomiting (CINV) remains common in patients with breast cancer despite standard antiemetic therapy. Essential oil-based interventions, including inhalation aromatherapy and essential oil-derived preparations, are increasingly used as supportive care, but their efficacy remains uncertain. METHODS: We conducted a systematic review and meta-analysis of RCTs comparing essential oil-based interventions with control conditions in adults with breast cancer receiving chemotherapy. PubMed, Embase, Cochrane CENTRAL, and Web of Science were searched through 14 February 2026. The acute phase was defined as within 24 h after chemotherapy. Continuous outcomes were pooled as Hedges' g standardized mean differences (SMDs) with 95% CIs using random-effects REML models. RoB 2, GRADE, and Knapp-Hartung sensitivity analyses were applied. RESULTS: Four RCTs were included. For acute nausea severity (4 RCTs, n = 336), essential oil-based interventions were associated with reduced symptoms versus control (SMD = -0.49, 95% CI -0.76 to -0.22; I2 = 35.42%). For vomiting frequency (2 RCTs, n = 144), the pooled effect was not significant (SMD = -0.25, 95% CI -0.75 to 0.25; I2 = 56.52%). For vomiting severity/score (2 RCTs, n = 192), a modest reduction was observed in the primary REML analysis (SMD = -0.31, 95% CI -0.59 to -0.03; I2 = 0%), but not after Knapp-Hartung adjustment. RoB 2 identified one study at low risk, two with some concerns, and one at high risk of bias. GRADE certainty was low for acute nausea and very low for vomiting outcomes. CONCLUSION: Essential oil-based interventions may reduce acute nausea in women with breast cancer receiving chemotherapy, but evidence remains limited, heterogeneous, and of low to very low certainty. Findings should be interpreted cautiously because the evidence included inhalation aromatherapy trials and one exploratory oral peppermint extract trial. These interventions should not replace guideline-based antiemetic therapy. Larger, well-designed RCTs with prospectively registered protocols are needed. SYSTEMATIC REVIEW REGISTRATION: https://www.crd.york.ac.uk/prospero/, identifier [CRD420261308323].