Codeine is changed to morphine in the body. Some people change codeine to morphine more quickly than others. These individuals are called ultra-rapid metabolizers of codeine. Contact your doctor immediately if you experience extreme sleepiness, confusion, or shallow breathing. NHS medicines information on codeine – what it's used for, side effects, dosage and who can take it. Codeine is a narcotic pain reliever (analgesic) used to treat mild to moderately severe pain frequently combined with Tylenol or aspirin. Common side effects include itching, rash, stomach pain, constipation, shortness of breath, nausea, lightheadedness, and dizziness. Codeine is used to manage mild to moderate pain, where treatment with an opioid is appropriate, and when other pain treatments such as non-opioid pain medicines do not treat your pain well enough or you cannot tolerate them. Codeine is an opioid and considered a strong prescription pain medicine. Codeine is a type of opioid (a strong painkiller) that is used to treat mild-to-moderate types of pain. It can be particularly useful when painkillers such as paracetamol and ibuprofen have not been effective. Codeine is an opiate and prodrug of morphine mainly used to treat pain, coughing, and diarrhea. It is commonly used as a recreational drug. Easy-to-read patient tips for codeine covering how it works, benefits, risks, and best practices. Codeine belongs to a class of medications called opiate (narcotic) analgesics and to a class of medications called antitussives. When codeine is used to treat pain, it works by changing the way the brain and nervous system respond to pain. View codeine phosphate information, including dose, uses, side-effects, renal impairment, pregnancy, breast feeding, contra-indications and important safety information. Find patient medical information for Codeine on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings.