Codeine or 3-methylmorphine (a naturally occurring methylated morphine) is an opiate used to treat pain, as a cough medicine, and for diarrhea. It is often sold as a salt in the form of either codeine sulfate or codeine phosphate in the United States, United Kingdom and Australia; codeine hydrochloride is more common worldwide and the citrate, hydroiodide, hydrobromide, tartrate, and other salts are also seen.Codeine is the second-most predominant alkaloid in opium, at up to three percent. Although codeine can be extracted from natural sources, a semi-synthetic process is the primary source of codeine for pharmaceutical use. It is considered the prototype of the weak to midrange opioids (tramadol, dextropropoxyphene, dihydrocodeine, hydrocodone, oxycodone).In 2013 about 361,000 kilograms of codeine were produced while 249,000 kilograms were used. It is the most commonly taken opiate. It is on the WHO Model List of Essential Medicines, a list of the most important medication needed in a basic health system.