Opioids (opiates) are also known as painkillers because of their analgesic, or pain-relieving, properties. This class of medications, also widely referred to as narcotics, is made up primarily of substances derived from opium, or artiﬁcially created analogs, and includes morphine, codeine, heroin, and related drugs. Morphine is frequently used before or after surgery to alleviate severe pain. Codeine, less effective than morphine, is prescribed for milder pain. Other widely prescribed opioids include oxycodone (recently in the news owing to abuse of its time-release form, OxyContin), propoxyphene (best known as Darvon), hydrocodone (best known as Vicodin), and meperidine (Demerol), which is used less often than the others because of its side effects. Codeine is also frequently used to treat coughs and is sometimes prescribed for serious diarrhea as well (all the opioids have constipating properties). The best-known illegal opiate, heroin, is actually the result of a failed experiment to produce a better medicine. It was introduced in 1896 by the Bayer Company, as a purer form of morphine that produced fewer side effects.
Opioids act by mimicking the actions of endorphins, naturally occurring neurotransmitters with just one job: inhibiting the transmittal of pain signals within the central nervous system. Because of the existence of endorphins, neurons in the brain and spinal cord (and, curiously, in the digestive tract) have specialized receptor sites for opioids. Opioid drugs simply attach to those receptors, thus halting the transmission of pain messages. In addition to pain relief, however, opiates can also produce constipation; cause drowsiness; and produce feelings of euphoria––this, more than pain relief, contributes to psychological dependence. When taken to excess, however, they can also act on brainstem areas that regulate respiration, depressing that function.
It is this ability to depress breathing that makes long-term abuse of opioids so dangerous. The fatal dose, the amount that will completely arrest respiration, remains fairly constant for each individual. As tolerance for the drug builds, larger and larger amounts are required to achieve the desired effect, but the fatal dose remains the same as the effective dose increases. Eventually, an addict will reach a point at which the effective dose exceeds the fatal dose. This is how accidental overdoses occur. In abusers of prescription opiates, accidental overdoses can also occur, but sometimes they happen after fairly short-term use, because the users simply take too much in their attempt to get high. This especially became a problem with the recent popularity of Oxycontin, which is used to treat severe chronic pain. Since the drug is intended to be released slowly into the bloodstream over a long period of time, each individual pill contains a much larger dose than typical painkiller tablets. Abusers frequently crush the pills and take it all at once, or even dissolve and inject it (this has led to the nickname “hillbilly heroin”), thus administering an unpredictably high dose that may be too much for them.
In addition to tolerance, long-term use of opioids also produces withdrawal symptoms if use of the drug is reduced or stopped. Opiate withdrawal can be severe, including insomnia, diarrhea, vomiting, pain, and cold ﬂashes—the poultry-like appearance of the resulting goose bumps may be the source of the term “cold turkey.” The sickness is severe enough to make quitting heroin very difﬁcult, even when the user is highly motivated to quit. For this reason, quitting heroin is often accompanied by administration of methadone, intended to be a less potent opioid, to reduce the severity of the withdrawal symptoms. Unfortunately, some addicts simply become addicted to the methadone instead, and withdrawal from it can be fairly unpleasant, too. It bears mentioning, however, that a large body of research has shown that when prescribed narcotics are managed and monitored properly, their use is safe and rarely results in addiction. This is good news, as opioids remain by far the most effective way to manage serious pain.
- Stimmel, B. Opiate Receptors, Neurotransmitters, and Drug Dependence: Basic Science-Clinical Correlates. Binghamton, NY: Haworth Press, 1981.