Chantix in Adult Smokers With Attention Deficit Hyperactivity Disorder (ADHD)

Inclusion Criteria: * Male and female outpatients from 18-60 years of age; * A cigarette smoking history of at least 3 months, and currently smoking; * An interest in quitting smoking and a willingness to comply with all study procedures and medication instructions; * A current DSM-IV-TR diagnosis of ADHD confirmed by clinical psychiatric evaluation and/or ADHD module of structured diagnostic interview, completed by study clinician. * For females of child-bearing potential: pregnancy test at screening visit is negative and the subject does not plan to become pregnant during the study. Exclusion Criteria: * Pregnancy or breast-feeding; * Clinically significant and/or unstable medical condition including renal, hepatic, or neurological, based upon a medical history and vital signs; * Ongoing treatment with medications which may be affected (altered blood levels) if subjects stop smoking in the study, including insulin, theophylline, and blood thinners, as determined by clinician; * Clinically significant cardiovascular history, including myocardial infarction, untreated hypertension, atrial fibrillation, or arrhythmia; * Current untreated psychiatric comorbidity which the investigator judges to be of greater than mild severity, including Major Depressive Disorder; * Current psychiatric comorbidity, including suicidality, homicidality, psychosis, determined by the clinician to be clinically significant and/or unstable * Lifetime history of DSM-IV Bipolar I disorder, Schizophrenia, or suicide attempt as determined through clinical evaluation or diagnostic interview; * Currently (within 3 months) meets DSM-IV criteria for abuse or dependence for any psychoactive substance other than nicotine; * Current treatment with mood stabilizers, anti-psychotics, nicotine replacement therapies, or varenicline; * Mental retardation (IQ \< 75); * History of intolerance or allergy to varenicline. * Clinically significant abnormal screening values including: * Consistent readings of hypertension (\>140/90) during screening period (including screening and baseline visits), defined as two or more readings (each being the average of three measurements) at a single visit with systolic blood pressure, SBP \> 140 and/or diastolic blood pressure, DBP, \> 90, and confirmed by manual reading. Subjects with isolated incidences (of triplicate average BP) of SBP \> 140 and/or DBP \> 90 at baseline/week 0 visit, confirmed by manual reading, which are determined to be clinically significant.