Publisher Summary This chapter reviews the various narcotic antagonists and analgesics. The reports of the chemistry and activities of ethenothebaines and oripavines include a collated review of structure–activity relationships. The importance of an R configuration at C19 for high analgesic activity has been established for the 7-β as well as the 7-α series. The benzmorphan analog was comparable to codeine in the acetic acid writing test, but eleven other analogs oxygenated at the carbon bearing the phenyl group were inactive. A series of anileridine derivatives bearing substituents with potential alkylating ability was made in order to investigate the possibility of locating analgesic receptors by specific alkylation. The fumaryl derivative caused apparent inactivation which could be prevented by naloxone pretreatment. WY-12157 showed analgesic activity of the order of morphine as did both of its optical isomers. It was not antagonized by naloxone and produced little or no tolerance, but central nervous system toxicity and blindness were seen during chronic administration to monkeys. Cyclazocine is a powerful antagonist and analgesic and it's many known analogs show both properties.