Codeine is a painkiller. It's used to treat pain, for example after an operation or an injury. It's also used for long-standing pain when everyday painkillers, such as aspirin, ibuprofen and paracetamol, haven't worked. What are over-the-counter (OTC) medicines? Over-the-counter (OTC) medicines are those that can be sold directly to people without a prescription. Dextromethorphan (DXM or DM) is a medication most often used as a cough suppressant in over-the-counter cold and cough medicines. It is sold in syrup, tablet, spray, and lozenge forms. Consumer information about the medication PROMETHAZINE/CODEINE SYRUP - ORAL (Phenergan w/ codeine), includes side effects, drug interactions, recommended dosages, and storage information. Read more about the prescription drug PROMETHAZINE/CODEINE SYRUP - ORAL. Easy-to-read patient leaflet for Promethazine and Codeine. Includes indications, proper use, special instructions, precautions, and possible side effects. Codeine is an opioid medication prescribed to reduce physical pain. It can cause feelings of relaxation, drowsiness, confusion, nausea, itchiness and constipation, especially if taken in large doses. For the Consumer. Applies to codeine / promethazine: oral syrup. Along with its needed effects, codeine/promethazine may cause some unwanted effects. Codeine is an opiate pain medication that's sometimes referred to as a narcotic. Its active ingredient is found in many different medications that treat pain, cough, and diarrhea. Codeine with promethazine is frequently prescribed to people to treat a wide variety of symptoms. Codeine with promethazine is a combination medicine that can treat the symptoms of the common cold, allergies, the flu, and various breathing illnesses like bronchitis and sinusitis. Codeine is an opiate used to treat pain, as a cough medicine, and for diarrhea. It is typically used to treat mild to moderate degrees of pain. Greater benefit may occur when combined with paracetamol (acetaminophen) or a nonsteroidal anti-inflammatory drug (NSAID) such as aspirin or ibuprofen. Evidence does not support its use for acute cough.