Codeine or 3-methylmorphine (a natural isomer of methylated morphine, the other being the semi-synthetic 6-methylmorphine) is an opiate used for its analgesic, antitussive, and antidiarrheal properties. Codeine is the second-most predominant alkaloid in opium, at up to three percent; it is much more prevalent in the Iranian poppy (Papaver bractreatum), and codeine is extracted from this species in some places although the below-mentioned morphine methylation process is still much more common. It is considered the prototype of the weak to midrange opioids (tramadol, dextropropoxyphene, dihydrocodeine, hydrocodone). Codeine is used to treat mild to moderate pain and to relieve cough. Codeine is also used to treat diarrhea and diarrhea predominant irritable bowel syndrome, although loperamide (which is available OTC for milder diarrhea), diphenoxylate, paregoric or even laudanum (also known as Tincture of Opium) are more frequently used to treat severe diarrhea.
Contributions by Galaxiaad, 18.104.22.168, and Beetstra.