The standard 12-week varenicline monotherapy used in this study did not have an exceptionally high abstinence rate, and thus likely did not produce a ceiling effect. The abstinence rate for participants in this group was similar to, or lower than, rates obtained with such treatment in prior studies. It is unclear why standard varenicline combination therapy orextended varenicline monotherapy produced some positiveeffects in prior trials but showed little evidence of enhancedeffectiveness in the present study.