Codeine is the most widely used, naturally occurring narcotic in medical treatment in the world. This alkaloid is found in opium in concentrations as much as 2.5 percent. However, most codeine used in the United States is produced from morphine. Codeine is also the starting material for the production of two other narcotics, dihydrocodeine and hydrocodone.

For use in suppressing coughs, codeine is found in a number of liquid preparations. Codeine is also used to a lesser extent as an injectable solution for treating pain. Codeine products are diverted from legitimate sources and are encountered on the illicit market.

Codeine is prescribed for the relief of pain as well as cough suppression. Compared to morphine, codeine produces less analgesia, sedation, and respiratory depression, and is usually taken orally. It is made into tablets either alone (Schedule II) or in combination with aspirin or acetaminophen (i.e., Tylenol with Codeine, Schedule III).