Background <p>Breast cancer (BC) is the second most common cancer globally and the most prevalent among women. Chemotherapy, a primary treatment, frequently induces distressing side effects like nausea and vomiting. This study evaluated the efficacy of Citrus aurantium inhalation aromatherapy in reducing chemotherapy-induced nausea and vomiting (CINV) in women with BC.</p> Methods <p>In this CONSORT-compliant parallel-group randomized controlled trial (registered at IRCT: 20240305061177N1), 92 BC patients at Motahari Clinic were randomly allocated (between April to August 2024) to an aromatherapy group (<i>n</i> = 46) or a control group (<i>n</i> = 46). Alongside standard antiemetic medications, the aromatherapy group inhaled two drops of C. aurantium essential oil applied to the philtrum, while the control group received sunflower oil. The Rhodes Index assessed nausea, vomiting, and retching over five days.</p> Results <p>Significant reductions in mean total scores for nausea, vomiting, and retching were observed in the aromatherapy group compared to the control group from days 3 to 5 (<i>P</i> &lt; 0.05), with no significant differences on days 1 and 2. Total symptom scores significantly decreased from Day 1 to Day 5 in the aromatherapy group while the control group showed no change.</p> Conclusion <p>C. aurantium aromatherapy significantly alleviated CINV during the delayed phase (days 3–5). Given its safety, affordability, and accessibility, this intervention offers a promising complementary approach for managing CINV in BC patients.</p> Trial registration <p>This trial was registered with the Iranian Registry of Clinical Trials (IRCT20240305061177N1, march 17, 2024).</p>