Chapter 11 The Opioids
• Narcotic Analgesics
• Opioid Receptors and Endogenous Neuropeptides
• Opioids and Pain
• Opioid Reinforcement, Tolerance, and Dependence
• Treatment Programs for Opioid Addiction
The opioid drugs are narcotic analgesics; they reduce pain without producing unconsciousness.
They create a sense of relaxation and sleep, and at high doses, can lead to coma and death.
They are the best painkillers known, and they also produce a sense of euphoria.
Opium is an extract of a poppy plant (Papaver somniferum).
Most comes from Southeast Asia, India, China, Iran, Turkey, and southeastern Europe.
Opiates have been used recreationally and in medicine for thousands of years.
• Figure 11.1 Preparing opium
Laudanum, an opium-based medicinal drink, was introduced in 1680 in England.
Drinking laudanum-laced wine was the accepted form of opium use in Victorian England and America.
Up to the twentieth century, laudanum was common in popular remedies.
The main active ingredient in opium is morphine. It was isolated in the early 1800s—the first time an
active ingredient of any medicinal plant was isolated.
This allowed doctors to prescribe it in known dosages.
Opium also contains codeine, thebaine, narcotine, and other ingredients.
Small differences in molecular structure determine effectiveness and side effects.
• Figure 11.3 Molecular structure of morphine, codeine, heroin, and naloxone Heroin was made by adding two acetyl groups to morphine, making it more lipid soluble.
This reaches the brain faster, so it is much more potent than morphine, when injected.
Other modifications produce partial agonists: they bind to the receptors but have less biological effect.
Pure antagonists, such as naloxone and nalorphine, are structurally similar but have no efficacy. They
can prevent or reverse the effect of opioids.
Some opium derivatives are “semi-synthetic”—chemically modified versions of opium ingredients.
Other narcotics are entirely synthetic and may have very different chemical structures.