Phenylephrine and promethazine is a combination medicine used to treat sneezing, runny nose, watery eyes, hives, skin rash, itching, and other cold or allergy symptoms. It is worth noting that Phenylephrine is a decongestant that shrinks blood vessels in the nasal passages. In fact, dilated blood vessels can cause stuffy nose. As for Promethazine, it is an antihistamine that reduces the effects of natural chemical histamine in the body. Bear in mind that Histamine can produce symptoms of sneezing, itching, watery eyes, and runny nose. Remember that you should not use the Phenylephrine- promethazine combination if you are allergic to either of these two medicines, or if you have asthma, high blood pressure, or coronary artery disease. As a matter of fact, it is not known whether this medicine will harm an unborn baby, or if it passes into breast milk. So, make sure you tell your doctor if you are pregnant or if you are breastfeeding. You must, however, stop using the Phenylephrine- promethazine combination medicine and call your doctor at once if you have seizure, weak or shallow breathing, confusion, hallucinations, or if you feel ill.