Promethazine Hydrochloride Suppositories 12.5 mg, 12 Count (Rx)*Refrigerated Item, Ships Next Day Air, Signature Required* Promethazine Hydrochloride Suppositories 12. 5 mg, commonly known as Promethazine Suppositories, is a medication that is primarily used to treat nausea and vomiting caused by various conditions such as motion sickness, chemotherapy, and anesthesia. It belongs to a class of drugs called phenothiazine antihistamines, which work by blocking the action of certain natural substances in the body