Learn about the side effects of codeine, from common to rare, for consumers and healthcare professionals. 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 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. Codeine is an opiate and prodrug of morphine mainly used to treat pain, coughing, and diarrhea. It is commonly used as a recreational drug. Codeine sulfate is an opioid analgesic indicated for the relief of mild to moderately severe pain where the use of an opioid analgesic is appropriate. Selection of patients for treatment with codeine sulfate should be governed by the same principles that apply to the use of similar opioid analgesics. Codeine is a mild opioid that relieves pain and suppresses coughing by binding to receptors in your brain and spinal cord. On its own, codeine is actually a prodrug, meaning your body must convert it into morphine before it produces most of its painkilling effect. Codeine is an alkaloid obtained from opium or prepared from morphine by methylation and occurs as white crystals. Codeine effloresces slowly in dry air and is effected by light. 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. Find patient medical information for Codeine on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings 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.