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.

Common side effects include vomiting, constipation, itchiness, lightheadedness, and drowsiness. Serious side effects may include breathing difficulties and addiction. It is unclear if its use in pregnancy is safe. Care should be used during breastfeeding as it may result in opiate toxicity in the baby. Its use as of 2016 is not recommended for children. Codeine works following being broken down by the liver into morphine. How quickly this occurs depends on a person's genetics.