 This study will consist of two study groups composed of 40 subjects each being randomized to receive either placebo or varenicline 0.5mg once daily for days 1-3, 0.5mg twice daily for days 4-7 followed by 1mg twice daily for days 8-14. One group will be heavy smokers and heavy drinkers while the other will be heavy smokers and social drinkers. Upon entering the study, subjects will undergo baseline cognitive and craving measures for both tobacco and alcohol associated cue presentations prior to randomization to varenicline or placebo. Subjects will be provided a 1-week supply of study medications and directions for use. During this period, subjects will be requested to complete a diary outlining their cigarette and alcohol craving and consumption each day and outline any adverse effects. Upon completion of this 1-week period, subjects will attend the Centre for Addiction and Mental Health CAMH where their old pill bottles and daily diaries will be collected and they will be supplied with study medication 1mg varenicline taken twice daily or placebo and daily diary for an additional week. At this visit, subjects will complete the symptom checklist. At the end of the second week of treatment, subjects will be requested to return to CAMH where craving for tobacco and alcohol and cue-reactivity will be assessed in a similar manner as to study day After study completion, all subjects will be given the option to continue with varenicline in a 12-week treatment plan through the Nicotine Dependence Clinic. 