Varenicline on Reward Responses and Cognition in Adolescent Smokers

Inclusion Criteria: * Between 16-19 years of age * Able to read and write English * Smoking 5 or more cigarettes on a daily basis, for at least one year * Not seeking smoking cessation treatment * Weighing \> 55 kg (121 lbs) Exclusion Criteria: * Current criteria for abuse or dependence on another psychoactive substance. * Current diagnosis of any clinical significant psychiatric disease like major depressive disorder, panic or anxiety disorder, psychosis, schizophrenia, bipolar disorder. * Those with a prior suicide attempt or with active suicidal ideation at baseline * Any regular use of any psychoactive drugs including anxiolytics and antidepressants * Pregnant or lactating girls: females of childbearing potential who are unwilling or unable to use an acceptable method of contraception from at least 14 days prior to study medication administration until 30 days after the last dose of study medication. Acceptable methods of contraception are: abstinence; any form of hormonal contraception such as Depo-Provera, daily oral contraceptive, transdermal patch, or Nuva-ring; intra-uterine device, sterilization; or double barrier contraception which is a combination of any two of the following methods: condoms, spermicide, diaphragm. * Evidence or history of clinically significant neurological, hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, or allergic disease. * History of prior use of or sensitivity to varenicline. * Color-blindness * History of significant head trauma * Metal in body * Other medical conditions contra-indicated for MRI * Past history of marked irritability or agitation when attempting to quit smoking, determined by the Minnesota Nicotine Withdrawal Questionnaire.