Chinese molasses, dreams, gong, O, skee, toys, zero. People who inject opium feel a rush of pleasure, followed by a dreamy, pleasant state in which they have little sensitivity to pain.

Opium is a narcotic drug that is obtained from the unripe seedpods of the opium poppy (Papaver somniferum), a plant of the family Papaveraceae. Opium is obtained by slightly incising the seed capsules of the poppy after the plant's flower petals have fallen. The slit seedpods exude a milky latex that coagulates and changes colour, turning into a gumlike brown mass upon exposure to air. This raw opium may be ground into a powder, sold as lumps, cakes, or bricks, or treated further to obtain such derivatives as morphine, codeine, and heroin.

Opiates exert their main effects on the brain and spinal cord. Their principal action is to relieve or suppress pain. Like all opiates, opium causes a pleasant, drowsy state, in which all cares are forgotten and there is a decreased sense of pain (analgesia). Immediately after injection, the feelings are most intense. This feeling is described as similar to a sexual orgasm. The drugs also alleviate anxiety; induce relaxation, drowsiness, and sedation; and may impart a state of euphoria or other enhanced mood.

Opiates also have important physiological effects; they slow respiration and heartbeat, suppress the cough reflex, and relax the smooth muscles of the gastrointestinal tract. Opiates are addictive drugs--i.e., they produce a physical dependence (and withdrawal symptoms) that can only be assuaged by continued use of the drug.

The poppy plant evolved to match the biology of their predator/pollinators by developing opium alkaloids, a compound that acts on a class of neurotransmitter receptors in the brain of mammals. Opiates act by binding to specific receptor melocules for the endorphin/enkephalin class of neurotransmittors in the brain. These are among the neurotransmittors that control movement, moods, and physiology. The pharmacologically active principles of opium reside in its alkaloids, the most important of which, morphine, constitutes about 10 percent by weight of raw opium. Other active alkaloids such as papaverine and codeine are present in smaller proportions. Opium alkaloids are of two types, depending on chemical structure and action. Morphine, codeine, and thebaine, which represent one type, act upon the central nervous system and are analgesic, narcotic, and potentially addicting compounds. Papaverine, noscapine (formerly called narcotine), and most of the other opium alkaloids act only to relax involuntary (smooth) muscles.

With chronic use, the body develops a tolerance to opiates, so that progressively larger doses are needed to achieve the same effect. The higher opiates--heroin and morphine--are more addictive than opium or codeine. The habitual use of opium produces physical and mental deterioration and shortens life. An acute overdose of opium causes respiratory depression which can be fatal.

Opiates achieve their effect on the brain because their structure closely resembles that of certain molecules called endorphins, which are naturally produced in the body. Endorphins suppress pain and enhance mood by occupying certain receptor sites on specific neurons (nerve cells) that are involved in the transmission of nervous impulses. Opiate alkaloids are able to occupy the same receptor sites, thereby mimicking the effects of endorphins in suppressing the transmission of pain impulses within the nervous system.

sources:
Kuhn, Cynthia, Scott Swartzwelder and Wilkie Wilson. Buzzed : the straight facts about the most used and abused drugs from alcohol to ecstasy. New York: W.W. Norton, 1998.

portions reprinted from:
"opium" Britannica.com. Vers. 2001
1999-2001. Encyclopædia Britannica.
1 Sep. 2000
(http://www.britannica.com/eb/article?eu="58641"&tocid="0"&query=opium)