Codeine is an opioid medication used to treat mild to moderate pain and suppress cough. It works by altering the way the brain and nervous system respond to pain and controlling coughing. Although less potent than stronger opioids, codeine can still cause drowsiness, constipation, and nausea. It should be used only as prescribed, as misuse can lead to dependence and other serious side effects. Always follow medical guidance to ensure safe and effective use.