Granisetron hydrochloride injection is a prescription medication used to prevent nausea and vomiting caused by chemotherapy and surgery. It belongs to a group of medications called serotonin 5-HT3 receptor antagonists. Granisetron hydrochloride injection works by blocking the action of serotonin, a natural substance produced in the body that can cause nausea and vomiting. It is given as an injection into a muscle or vein. Common side effects may include headache, constipation, and fatigue.