Promethazine is used to prevent and treat nausea and vomiting related to certain conditions (such as before/after surgery, motion sickness). It is also used to treat allergy symptoms such as rash, itching, and runny nose. It may be used to help you feel sleepy/relaxed before and after surgery or to help certain opioid pain relievers (such as meperidine) work better. It may also be used for a short time to treat a runny nose due to the common cold.