Promethazine is a first-generation antihistamine. It is used to treat allergies, trouble sleeping, and nausea. It may help with some symptoms associated with the common cold. It may also be used for sedating people who are agitated or anxious.It is available by mouth as a syrup, as a rectal suppository, or by injection into a muscle.

Common side effects include confusion and sleepiness. Alcohol or other sedatives can make this worse. It is unclear if use during pregnancy or breastfeeding is safe for the baby. Use is not recommended in those less than two years old due to potentially negative effects on breathing. Use by injection into a vein is not recommended due to potential skin damage. It is in the phenothiazine family of medications.
Promethazine was made in the 1940s by a team of scientists from Rhône-Poulenc laboratories. It was approved for medical use in the United States in 1951.It is a generic medication and is available under many brand names globally.The wholesale cost of the by mouth formulation is less than US$0.20 per dose as of 2018.In the United Kingdom this dose costs less than £0.25.In 2017, it was the 147th most commonly prescribed medication in the United States, with more than four million prescriptions.