Analgesic nitrous oxide in neuropsychiatry: past, present and future.

We highlight the distinction between analgesic and anesthetic concentrations of nitrous oxide, with special reference to the safety of analgesic nitrous oxide. We present evidence that the gas at analgesic concentrations is an opioid agonist. Its extremely low abuse potential, despite its opioid properties, is discussed with regard to its evanescent action and possible partial agonistic effects, making it the least addictive of all mind-altering addictive substances. The activities of analgesic nitrous oxide make it an almost ideal agent with which to investigate the functions of the opioid system in man. We also discuss its use as a diagnostic and therapeutic agent in neuropsychiatry.