A drug used alone or with other drugs to prevent nausea and vomiting caused by chemotherapy. Granisetron blocks the action of the chemical serotonin, which binds to certain nerves and may trigger nausea and vomiting. Blocking serotonin may help lessen nausea and vomiting. Granisetron is a type of serotonin receptor antagonist and a type of antiemetic. Also called Sancuso and Sustol.