Heroin and Endorphin Research:
Researchers have discovered that the body naturally manufactures chemicals called endorphins to maintain a general sense of wellbeing in humans and to regulate certain bodily functions. When the body experiences pain or stress, it releases large quantities of endorphins to kill pain. Additional research revealed that opium and human endorphins are identical to one another in their molecular makeup and, therefore, in their effects on the body. Thus, not only is heroin able to perfectly mimic the effects of endorphins, but since the drug's molecules are usually present in far greater quantities than those of naturally occurring endorphins, its effects on the body are considerably stronger.
Endorphin researchers have also found that as a user's body attempts to adapt to the near-constant presence of heroin, significant chemical and physical changes take place in the brain. The brain senses an overabundance of what it thinks are endorphins, and attempts to restore balance to itself by shutting down its own production of real endorphins. It continues to do so whether or not the addict is currently high on heroin. The addict's body must therefore depend entirely on heroin to regulate the various bodily functions that are no longer regulated by endorphins. When there is no heroin present, these functions cease to operate properly, thereby triggering the wide variety of symptoms associated with withdrawal.
Another way that the heroin addict's body attempts to restore balance to itself is by making its various systems, including the nervous system, resistant to the effects of heroin. This resistance to the drug's effects, known as "tolerance," steadily increases for as long as the addict continues to use the drug without interruption. As an addict's tolerance increases, so does the amount of heroin needed to produce the drug's original effects. The severity of withdrawal symptoms likewise increases. Tolerance to heroin increases extremely quickly and causes the need for dosages that would easily cause lethal overdose in first-time users. For example, while first-time users may need as little as two to five milligrams to get high, long-term addicts typically need hundreds of milligrams a day just to take the edge off their withdrawal symptoms. (An addict never grows immune to overdose, however—some amount of heroin will always prove fatal.) Once addiction has progressed to a relatively high point of tolerance, most addicts switch to intravenous heroin injection to get the strongest possible dosage, and this form of drug use exposes them to an enormous array of illnesses. "To know . . . an injecting drug user as a patient," explains Dr. Gabor D. Kelen of Johns Hopkins University School of Medicine, "is to know medicine, because they pretty well get just about every possible medical condition known to man."