The purpose of this study is to examine how smoking cessation medications (varenicline, bupropion) affect the ability to resist smoking and also subsequent ad-lib smoking in non-treatment seeking daily smokers.

Inclusion Criteria:

• ages 18-55
• able to read and write in English
• Smokers

Exclusion Criteria:

• any significant current medical or psychiatric conditions that would contraindicate smoking
• current Diagnostic and Statistical Manual IV abuse or dependence of other substances, other than nicotine dependence or alcohol abuse
• positive test result at intake appointments on urine drug screens conducted for opiates, cocaine, or benzodiazepines
• women who are pregnant or nursing
• suicidal, homicidal, or evidence of current severe mental illness
• participants prescribed any psychotropic drug in the 30 days prior to study enrollment
• blood donation within the past 6 weeks
• individuals seeking treatment for smoking cessation or have attempted to quit smoking within the past 3 months
• specific exclusions for bupropion administration not already specified, including: have taken monoamine inhibitors in the past 6 weeks; history of anorexia or bulimia; previous hypersensitivity to bupropion; history of alcohol or drug dependence in the past year; history of seizure disorder of any etiology
• known allergy to varenicline or taking H2blockers
• participation within the past 8 weeks in other studies that involve additive blood sampling and/or interventional measures that would be considered excessive in combination with the current study

Titration period (7 days)

All adverse events reported during 1 week medication period. Baseline reporting not controlled. Subjects were queried about the presence/absence of severity of common symptoms (>5% from placebo according to manufacturer) associated with varenicline and bupropion. Adverse events assessed on Day 2 and Day 8.