Figure 1.

Plasma nicotine and expired carbon monoxide (CO) concentration. Mean (±standard error of the mean [ SEM ]) plasma nicotine (Panel A) and expired CO concentration (Panel B) for 22 experienced waterpipe users before and immediately after (Panel A) or 5 and 15 minutes after (Panel B) smoking waterpipe during a 45-minute ad libitum session as part of a dyad (circles) or as a singleton condition (squares). The 45-minute smoking period is denoted by the black bar parallel to the X-axis. Filled symbols indicate a significant difference from baseline; asterisks (*) indicate a significant difference between singleton and dyad conditions at that time point.