II.

Opioids

This class includes drugs derived from opium, such as morphine and heroin, and synthetic substitutes such as methadone. Medically, morphine is a potent pain reliever; indeed, it is the standard by which other pain-relieving drugs are measured (see Narcotics). Morphine and other opium derivatives also suppress coughing, reduce movements of the intestine (providing relief from diarrhea), and induce a state of psychological indifference. Heroin, a preparation synthesized from morphine, was introduced in 1898 as a cough suppressant and nonaddictive substitute for morphine. The addictive potential of heroin, however, was soon recognized, and its use was prohibited in the United States, even in medical practice. Users report that heroin produces a “rush” or “high” immediately after being taken. It also produces a state of profound indifference and may increase energy.

Opioids produce different effects under different circumstances. The drug user’s past experience and expectations have some influence, as does the method of administering the drug (by injection, ingestion, or inhalation). Symptoms of withdrawal from opioids include kicking movements in the legs, anxiety, insomnia, nausea, sweating, cramps, vomiting, diarrhea, and fever.

In the 1970s scientists isolated substances called enkephalins, which are naturally occurring opiates in the brain. They discovered what many believe is the reason behind physical dependence on opioids—that is, the drugs may mimic the action of enkephalins. If true, this hypothesis suggests that physical dependence on opioids may develop in people who have a deficiency of these natural substances.