Figure 1

Self-reported drug effect. Self-reported strength of drug effect of 0%, 20% or 40% N₂O is shown as a function of time. The solid bars indicate the average response time; whiskers indicate SD. PRE refers to the measure taken at baseline; IA refers to the averaged value during inhalation; 1, 3, 5, and 7 refer to hours after inhalation ceased. An asterisk represents a significant difference between a value at a given concentration at a particular time during inhalation and the lower adjacent concentration at the same time point.