Narcotics are addictive drugs that are valuable for providing pain relief; they are often called opioids because they were originally made from opium, a natural plant substance. There are now many man-made chemicals, similar to the natural opioids, that are used therapeutically for pain relief. Virtually all narcotics cause side effects that include drowsiness, addiction, constipation, nausea, vomiting and slowing of breathing. All these drugs work by binding to specific receptors on nerve cells that are associated with the sensation of pain. Some, called agonists, work to activate such receptors, while some, called antagonists, block certain receptors. Others, called mixed agonist-antagonist drugs, activate some receptors associated with pain while blocking others.
Natural Narcotic Drugs
Two natural narcotic drugs purified from opium obtained from the Asian poppy are morphine, the stronger of the two, and codeine. (ref 4) Morphine (Kadia, Avinza, Embeda, MS-Contin) is used to relieve cancer pain, pain after major surgery, and heart attack pain, and for relieving breathlessness at the end of life in terminal patients. Codeine, often found in combination with other pain relievers such as acetaminophen, is used for less severe pain, for example after minor injury or surgery, and as a cough-suppressant. People who use these drugs over time develop physical dependence, which means that when the drug is stopped there are withdrawal symptoms including agitation, pain, insomnia, diarrhea, sweating, and rapid heart beat.
Synthetic Narcotic Drugs
Heroin and hydromorphone (Dilaudid) are synthetic narcotics, made from modifying morphine in a laboratory. Other similar drugs include oxycodone (OxyContin, Percocet) and hydrocodone (Vicodin, Lortab, Norco); both are used for pain from injuries. Other narcotics are completely synthetic. One is fentanyl (Sublimaze, Actiq, Durogesic) and is used in anesthesia, sedation in intensive care units and in long-acting patches for cancer pain. Other synthetic narcotics are meperidine (Demerol), used for post-surgical pain, and methadone (Dolophine), used as a heroin substitute during withdrawal treatment. (refs 1,3)
Agonist Narcotic Drugs
When narcotics bind to their receptors they inhibit the electrical activity of certain nerve cells in complex nerve networks, thereby reducing the amount of pain information reaching the brain. Other results of such receptor activity can contribute to the feeling of euphoria and/or drowsiness and the slowing down of breathing. Binding of narcotics to receptors in the intestine causes constipation.
More Complex Receptor Interactions of Narcotics
Some narcotic drugs can work as described above on pain reception, but then by blocking other receptor types, or by acting only as partial agonists on some types of opioid receptors, can minimize problematic side effects like drowsiness, constipation, addiction and respiratory depression. Examples of these narcotics are buprenorphine (Butrans), pentazocine (Talwin), nalbuphine (Nubain) and butorphanol (Stadol). These drugs can provide, for example, good pain relief with less risk of inadequate breathing. Ongoing work to synthesize new narcotics is aimed at finding drugs that give excellent pain relief while further minimizing the troubling side effects found in the existing drugs.