The principle active ingredient found in OPIUM, the extract of the poppy plant. Morphine is named after the Greek god Morpheus, the god of dreams. Morphine, a NARCOTIC ANALGESIC (see ANALGESIA; NARCOTICS), is a potent opiate drug that has a number of physiological effects. It can induce sleepiness and relaxation, suppress respiration, increase PAIN threshold, and cause a profound sense of well-being and EUPHORIA. These latter reinforcing properties lead to SELF-ADMINISTRATION of morphine. Use of the opium extract for its psychological and medicinal properties may date back over 5000 years. References to opium use are found in the writings of early Egyptian, Greek, Roman, Arabic and Chinese cultures. In the nineteenth century, opium (in the form of LAUDANUM, a potion containing opium) became an important part of the pharmacopoeia in England and America. One of the most famous descriptions of the properties of morphine is provided by Thomas De Quincey (1785–1859) who wrote an essay, Confessions of an English Opium-Eater, in 1821. He first took opium for a toothache and wrote: ‘In an hour, O heavens! What a revulsion! What a resurrection from its lowest depths, of the inner spirit!… That my pains had vanished was now a trifle in my eyes; this negative effect was swallowed up in the immensity of those positive effects which had opened before me, in the abyss of divine enjoyment thus suddenly revealed…here was the secret of happiness, about which philosophers had disputed for so many ages, at once discovered; happiness might now be bought for a penny, and carried in the waistcoat pocket; portable ecstasies might be had corked up in a pint-bottle and peace of mind might be sent down by the mail.’
However, while the pain-relieving effects of opiates were much appreciated, the dangers and addictive properties also became clear as its use spread throughout societies (see ADDICTION). Morphine has high ABUSE POTENTIAL; with repeated use, individuals can become addicted to the drug. Morphine addiction is associated with a need for the drug to function normally, intense drug craving, and a withdrawal syndrome following abstinence from the drug. Morphine is also self-administered by animals. Much of what is known about the brain’s endogenous OPIOID PEPTIDES, the ENDORPHINS and ENKEPHALINS, has been derived from studies of morphine’s effects in animals.
Morphine is the most commonly used drug in the treatment of pain. A number of physiological symptoms result from morphine administration, which are the consequence of the drug acting in several brain regions. The main physical effects morphine has is to reduce pain perception. Morphine commonly causes NAUSEA and VOMITING, particularly with initial use. It also causes a marked constriction of the pupil, known as ‘pinpoint pupil’. This sign is commonly seen in HEROIN addicts (heroin being a semi-synthetic derivative of morphine). Opiates slow the movement of food through the digestive tract and thus cause constipation. The most dangerous physiological effect is respiratory depression, respiratory arrest being the most common cause of death from overdose.
Morphine DEPENDENCE may be associated with a high degree of TOLERANCE and physical dependence. With repeated use, the dose taken by the user gradually becomes higher. However, tolerance develops to some effects of opiates and not to others. For example a remarkable degree of tolerance may be exhibited to the respiratory depressant, sedative, analgesic, nauseating and euphoric effects while little tolerance is seen to the constipating and pupil-decreasing effects. Physical dependence is also classically associated with opiate addiction, and a WITHDRAWAL SYNDROME results in dependent individuals upon cessation of the drug. It is not known what particular factors determine whether a person, once exposed to morphine or other opiates, will become dependent. As is true with all drugs with abuse potential, some people can experiment or be exposed to morphine and not develop a habit, while others become addicted. Many factors, including social environment, drug availability and psychological state may determine the pattern of drug use.
ANN E.KELLEY
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