Fig. 1. Study design.

All participants completed 6 scanning sessions; the current study reports data from the four completely counterbalanced sessions (sessions 3–6). At three points during a varenicline administration regime, (i.e., pre-pill, 2 weeks varenicline pill, 2 weeks placebo pill), participants were scanned twice, once wearing a nicotine patch and once wearing a placebo patch. Non-smokers received a 7-mg nicotine patch dose, while smokers received a dose that matched daily nicotine intake (21, 28, 35, or 42 mg patches for 10–15, 16–20, 21–25, and >25 cigarettes/day, respectively). Smokers were 12 h abstinent from nicotine (verified through CO levels). **Varenicline and placebo pill sessions were separated by >2 weeks. *Nicotine and placebo patch scans were separated by an average of 2.9 ± 1.7 days. #No washout interval separated medication periods. Double-headed arrows indicate randomized and counterbalanced order of the sessions. Figure reproduced with permission from Sutherland et al. [49].