Tolerance and physical dependence develop rapidly in the user. This alkaloid is found in opium in concentrations ranging from 0.7 to 2.5 percent. Most codeine used in the United States is produced from morphine. Compared to morphine, codeine produces less analgesia, sedation and respiratory depression, and is frequently taken orally. Codeine is medically prescribed for the relief of moderate pain.
Codeine is an effective cough suppressant and is found in a number of liquid preparations.
Codeine products are also used to a lesser extent as an injectable solution for the treatment of pain. It is by far the most widely used naturally occurring narcotic in medical treatment in the world. A minor constituent of opium, thebaine, is chemically similar to both morphine and codeine, but produces stimulatory rather than depressant effects. Thebaine is not used therapeutically, but is converted into a variety of compounds including codeine, hydrocodone, oxycodone, oxymorphone, nalbuphine, naloxone, naltrexone and buprenorphine. It is controlled in Schedule II of the CSA as well as under international law.