This combination medication is used to treat symptoms caused by the common cold, flu, allergies, or other breathing illnesses (e.g., sinusitis, bronchitis). Promethazine is an antihistamine that relieves watery eyes, itchy eyes/nose/throat, runny nose, and sneezing. Codeine is a narcotic cough suppressant (antitussive) that affects a certain part of the brain, reducing the urge to cough.