Promethazine comes as the brand names Phenadoz® and Phenergan®. Your doctor may have prescribed promethazine for you as a tablet, liquid, or rectal suppository form to treat your symptoms. Your doctor will tell you how much to take and how often. It is important to carefully follow your doctor's instructions for taking promethazine. Never take more promethazine than prescribed. Do not take extra promethazine to make up for a missed dose.