An adjusting-dose procedure for assessing the reinforcing effects of nitrous oxide with humans

Despite continued abuse, there is a paucity of empirical investigations on inhalants as reinforcers. The present study attempted to derive a method for studying the reinforcing effects of nitrous oxide (N2O) with human participants. An adjusting-dose procedure was employed to assess choice allocation for inhalation periods of varying doses of N2O. After experiencing the experimental parameters in forced-choice trials, participants made choices between a fixed dose of 0% N2O (i.e., 100% O2) and an adjusting dose of N2O (0-50% N2O in O2). The adjusting dose titrated as a function of the participant's choices. Conditions were run to stability and systematically replicated within-subject. Stable choice allocation served as both the chief dependent variable and an indication of the optimal reinforcing dose of N2O for that participant. Consistent with previous research on N2O, there was between-subject variability in the reinforcing effects of N2O; however, stable within-subject choice allocation was observed for 6 out of 8 participants. This method of assessing drug choice in humans allows for the testing of multiple doses within-subject, which is imperative, given that the reinforcing effects of drugs are known to vary across subjects and as a function of dose.