The oripavine derivative etorphine is a representative of a particularly potent class of morphine analogues. Etorphine is approximately 1000 times as potent as morphine, and arguably is too potent to be released for human therapy. It is currently used as a tranquilizer for large animals. There are two agents in the morphine class which are marketed as morphine antagonists . These agents, naloxone and naltrexone, are shown below.
Naloxone is a pure antagonist , and is commonly used to treat narcotic overdose.
Naltrexone is a similar agent, but does possess weak agonist activity , and is used to treat former narcotic addicts. As you will see later, there are some exceptions to this rule. A tertiary nitrogen with a small alkyl substituent. A quaternary carbon. A phenyl group or its isosteric equivalent directly attached to the quaternary carbon.