Prior to each deprivation session, participants were instructed to refrain from smoking for 12 hr. Compliance with nicotine deprivation instructions was assessed using expired CO (<=10 ppm) to confirm abstinence. Non-abstinent participants in the deprived condition were rescheduled. However, an exception was made where a CO above 10 ppm could be expected after a period of overnight deprivation. In this case, a value at or below 50% of their baseline CO was used as a cutoff point. The distribution of the CO values and our approach to the analyses involving expired CO and deprivation are discussed in the results section.
