, 2006). Two behavioral measures were administered to assess smoking reward before (study Day view more 1) and after 1 week of medication exposure (study Day 7). The Cigarette Purchase Task (CPT; MacKillop et al., 2008) is based on a model of drug reward assessment that has been successfully used with several drugs including heroin (Jacobs & Bickel, 1999; Petry & Bickel, 1998), tobacco (Jacobs & Bickel, 1999; MacKillop et al., 2008; Madden & Kalman, 2010), and alcohol (MacKillop et al., 2008; Murphy & MacKillop, 2006; Murphy, MacKillop, Skidmore, & Pederson, 2009). Participants indicated how many cigarettes they would purchase at each of the following 18 prices: 0.01, 0.5, 0.1, 0.3, 0.5, 1, 2, 3, 4, 5, 6, 11, 35, 70, 140, 280, 560, and 1120 US $/cigarette.

The simulated cigarette consumption data allow for analysis of behavioral economic demand curves. This method provides a framework for quantifying multiple dimensions of drug reinforcement (e.g., Bickel & Madden, 1999; Johnson & Bickel, 2006) and has been identified as an increasingly important framework for assessing drug abuse liability (Carter & Griffiths, 2009; Hursh, Galuska, Winger, & Woods, 2005). Specifically, demand functions were fit to these data (see Data Analysis section), resulting in two quantified parameters: demand intensity (Q0), which is the number of cigarettes purchased as price is close to zero (preferred level of consumption with no price constraint), and demand elasticity (��), which is price sensitivity (the extent to which increases in cigarette price result in decreases in cigarette purchases).

A Progressive Ratio Task (PRT) was also conducted on study Days 1 and 7. Progressive ratio procedures are standard drug reinforcement assessments, where research subjects must perform behavioral response requirements, on a schedule of increasing magnitude, GSK-3 in order to obtain a fixed dose of a test drug. Behavioral response requirements in this study were 100, 300, 600, 1,000, 1,500, 2,100, 2,800, 3,600, 4,500, 5,500, 6,600, and 7,800 computer mouse clicks, and participants immediately received one puff from a preferred-brand cigarette following the completion of each response requirement. Participants had 2 hr to complete as many responses as desired but could not leave the laboratory until the 2-hr time limit had expired. The primary task outcome is the breakpoint or highest response requirement completed in order to obtain a cigarette puff.