This Ondansetron and Ranitidine Tablets medication is used alone or with other medications to prevent nausea and vomiting caused by cancer drug treatment (chemotherapy) and radiation therapy. It is also used to prevent and treat nausea and vomiting after surgery. It works by blocking one of the body’s natural substances (serotonin) that causes vomitingIf you are using the liquid form of this medication, use a special measuring spoon or device to measure out your prescribed dose. Do not use a household spoon because you may not get the correct dose.