What is promethazine? Promethazine is in a group of drugs called phenothiazines (FEEN-oh-THYE-a-zeens). It works by changing the actions of chemicals in your brain. Promethazine also acts as an antihistamine. It blocks the effects of the naturally occurring chemical histamine in your body. Promethazine is used to treat allergy symptoms such as itching, runny nose, sneezing, itchy or […]