Background <p>Guideline-consistent prophylaxis is more effective in managing chemotherapy-induced nausea and vomiting than non-guideline approaches. However, the extent to which patients undergoing anticancer treatment receive guideline-recommended antiemetic therapy in real-world clinical practice remains unclear. This study evaluated the real-world patterns of antiemetic therapy among patients undergoing high emetic risk chemotherapy (HEC) and carboplatin-based moderate emetic risk chemotherapy (MEC) according to cancer type and treatment regimen and identified factors associated with antiemetic use.</p> Methods <p>We used health service utilization data linked to hospital-based cancer registries from 601 hospitals in Japan. Data from patients aged ≥ 18&#xa0;years diagnosed with cancer in 2020 and 2021 and treated with intravenous HEC or carboplatin-based MEC were analyzed. The percentage of patients prescribed antiemetics was calculated. A multilevel mixed-effects logistic regression was performed to identify factors associated with antiemetic therapy.</p> Results <p>A total of 157,705 patients were analyzed (HEC: 100,163; MEC: 57, 542). Triple-drug antiemetics (an NK₁ receptor antagonist, a 5-HT₃ receptor antagonist, and dexamethasone) were prescribed to 70.6% and 71.9% of patients undergoing HEC and MEC, respectively. In the HEC group, 8.9% received olanzapine in addition to triple-drug antiemetics. Antiemetic therapy varied by cancer type and regimen. In multilevel analysis, odds of receiving triple-drug antiemetics were the highest in small-cell lung cancer (OR = 3.065) for HEC and in endometrial cancer (OR = 1.324) for MEC.</p> Conclusion <p>Antiemetic therapy for patients receiving HEC or carboplatin-based MEC varies by cancer type and treatment regimen. Future research should explore reasons for and barriers to non-adherence to guidelines.</p>