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Opium is a narcotic drug, which is obtained from the unripe seed pods of the opium poppy (Papaver somniferum). To harvest opium, the skin of the ripening pods is scored by a sharp blade. The slashes exude a white, milky latex, which dries to a sticky brown material that is scraped off the pods as raw opium. Opium is highly physically addictive and its pharmacological action occurs because it binds to endorphin receptors in the brain. The mechanism of addiction and tolerance results from changes in nervous system receptors in response to the drug.
Opium has been a major item of trade for centuries, and widely used as a painkiller and sedative. Many patent medicines of the 19th century were based around laudanum (a solution of opium in alcohol). Opium can also be smoked, sometimes in combination with tobacco. In the 19th century, the attempt by China to stop the British trade in this form of opium from India was the cause of the Opium Wars, which led to Britain acquiring Hong Kong.
There were no legal restrictions on the importation or use of opium in the United States until the Harrison Narcotics Tax Act of 1914. Medicines often contained opium without any warning label. Today, there are numerous national and international laws governing the production and distribution of narcotic substances.
Although opium is used in the form of paregoric to treat diarrhea, most opium imported into the United States is broken down into its alkaloid constituents. These alkaloids are divided into two distinct chemical classes, phenanthrenes and isoquinolines. The principal phenanthrenes are morphine, codeine, and thebaine, while the isoquinolines have no significant central nervous system effects and are not regulated under the Controlled Substances Act. Opium is also illegally processed into heroin, and most current drug abuse occurs with processed derivatives rather than with raw opium.
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