SN instructed about Acetaminophen/codeine is a combination medication used to help relieve mild to moderate pain. It contains an opioid pain reliever (codeine) and a non-opioid pain reliever (acetaminophen). Codeine works in the brain to change how your body feels and responds to pain. Acetaminophen can also reduce a fever. Potential side effects are nausea, vomiting, constipation, lightheadedness, dizziness, or drowsiness may occur.