Codeine is mainly used to relieve mild to moderate pain. It relates to the group of drugs called narcotic analgesics (pain drugs). This medication acts on the CNS (central nervous system) to relieve pain. Few people use non-prescribed codeine medicine as a coping mechanism for chronic pain, mental health issues such as anxiety or depression, or to get high. In Australia, codeine is the most commonly used opioid and can no longer be purchased over the counter.