Codeine 300-30 mg is a combination medication that packs 300 mg of acetaminophen, which is a non-opioid pain reliever, along with 30 mg of codeine phosphate, an opioid. This medication is typically prescribed for moderate to moderately severe pain when other single-ingredient options just don’t cut it. Acetaminophen works to ease pain and reduce fever, while codeine changes the way your brain processes pain and can also help with coughing.