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
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