This will be a double-blind, placebo-controlled study that tests the effects of a 7-day treatment with 600 mg mifepristone, or placebo, on cognitive function, tobacco withdrawal severity and smoking behavior. Once the intake and physical examination is completed and eligibility is determined, subjects will participate in a baseline session to become familiar with the study procedures and to assess baseline measures of withdrawal, smoking urges, pain sensitivity, and cognitive performance. Subjects will be asked to refrain from consuming alcoholic beverages and drugs during their study participation. This will be verified by urine drug screening and breathalyzer before the session and during outpatient visits. If results indicate non-compliance with these study procedures, subjects will be discharged from the study.