Opioid agonist and antagonist drugs
The word opioid refers to derivatives of the opium plant or to syn-thetic drugs that imitate natural narcotics. Opioid agonists (also called narcotic agonists) include opium derivatives and synthetic drugs with similar properties. They’re used to relieve or decrease pain without causing the person to lose consciousness.
Some opioid agonists may also have antitussive effects that suppress coughing and antidiarrheal actions that can control diar-rhea.
Opioid antagonists aren’t pain medications. Instead, they block the effects of opioid agonists and are used to reverse adverse drug reactions, such as respiratory and CNS depression, produced by those drugs. Unfortunately, by reversing the analgesic effect, they also cause the patient’s pain to recur.
Some opioid analgesics, called mixed opioid agonist-antago-nists, have agonist and antagonist properties. The agonist compo-nent relieves pain, while the antagonist component decreases the risk of toxicity and drug dependence. These mixed opioid agonist-antagonists reduce the risk of respiratory depression and drug abuse.