Promethazine is used to relieve the symptoms of allergic reactions such as allergic rhinitis (runny nose and watery eyes caused by allergy to pollen, mold or dust), allergic conjunctivitis (red, watery eyes caused by allergies), allergic skin reactions, and allergic reactions to blood or plasma products. Promethazine is used with other medications to treat anaphylaxis (sudden, severe allergic reactions) and the symptoms of the common cold such as sneezing, cough, and runny nose. Promethazine is also used to relax and sedate patients before and after surgery, during labor, and at other times. Promethazine is also used to prevent and control nausea and vomiting that may occur after surgery, and with other medications to help relieve pain after surgery. Promethazine is also used to prevent and treat motion sickness. Promethazine helps control symptoms, but will not treat the cause of the symptoms or speed recovery. Promethazine is in a class of medications called phenothiazines. It works by blocking the action of a certain natural substance in the body.