A drug used with other drugs to prevent nausea and vomiting caused by chemotherapy. It is also used to prevent nausea and vomiting after surgery. Aprepitant blocks the action of a certain chemical in the brain that may trigger nausea and vomiting. Blocking this chemical may lessen nausea and vomiting. Aprepitant is a type of antiemetic and a type of substance P/neurokinin 1 receptor antagonist. Also called Emend.