Within- and between-subject variability in the reinforcing and subjective effects of nitrous oxide: in healthy volunteers

Within- and between-subject variability in the reinforcing and subjective e ffects of nitrous oxide (N2O) was studied across five sessions. Twelve volu nteers with no history of drug dependence sampled 30% N2O and 100%, oxygen for 10 min each, then chose nine times, once every 5 min, among N2O (e.g. ' Agent A'). oxygen (e.g. 'Agent B I), or 'drug-free air.' Choice varied acro ss subjects but was stable within subjects. Quantitative differences in sub jective effects occurred within and across subjects. Some subjective effect s were correlated with choice and/or differed between subjects who were con sistent choosers of N2O versus those who were not. However. drug liking and euphoria, two face-valid measures of abuse liability, were unrelated to ch oice. Thus, the present study found individual differences (i.e. between-su bject variability) in subjective and reinforcing effects of N2O and, in ter ms of within-subject variability, suggested that subjective effects fluctua te across sessions to a relatively greater extent than do reinforcing effec ts. The varying degrees of correlation between N2O choice and its subjectiv e effects emphasize the need for obtaining multiple measures when character izing abuse liability of this drug. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.