Rolapitant hydrochloride hydrate is primarily used as an antiemetic to prevent nausea and vomiting caused by chemotherapy, particularly in cancer patients undergoing highly emetogenic chemotherapy regimens. It works by selectively inhibiting the neurokinin-1 (NK1) receptor, which plays a key role in the body's vomiting reflex. This medication is often administered in combination with other antiemetic drugs, such as dexamethasone and a 5-HT3 receptor antagonist, to enhance its effectiveness. It is typically given orally as a single dose prior to chemotherapy, providing long-lasting protection against delayed-phase chemotherapy-induced nausea and vomiting (CINV), which can occur 24 hours or more after treatment. Its use significantly improves the quality of life for patients by reducing the debilitating side effects of chemotherapy.