Reinforcing effects of extended inhalation of nitrous oxide in humans.

The subjective, psychomotor and reinforcing effects of nitrous oxide at subanesthetic doses (30% and 40% in oxygen) were determined in normal healthy volunteers using a choice paradigm. Thirty percent nitrous oxide was chosen no more often than oxygen (41.6% choice rate), indicating that, for most of the subjects tested, extended inhalation of this nitrous oxide concentration was no more reinforcing than oxygen inhalation. Forty percent nitrous oxide was chosen significantly less often than oxygen (22% choice rate), indicating that, for most of the subjects tested, extended inhalation of this nitrous oxide concentration was less reinforcing than oxygen. Nitrous oxide produced robust subjective effects (e.g., increased ratings of 'high,' 'tingling,' and 'dizzy'). Subjects who chose nitrous oxide reported pleasant subjective effects and liked it, while those who chose placebo reported unpleasant subjective effects and disliked it. Both concentrations of nitrous oxide impaired psychomotor performance in all subjects. The lack of reinforcing effects noted in the present study, given nitrous oxide's known abuse potential, is discussed.