Modeling Stress-precipitated Smoking Behavior for Medication Development

Inclusion Criteria: * ages 18-60 * able to read and write in English * smokers Exclusion Criteria: * any significant current medical conditions that would contraindicate smoking * current Diagnostic and Statistical Manual IV (DSM-IV) abuse or dependence of other substances, other than nicotine (or caffeine) dependence * 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 severe mental illness * participants prescribed any psychotropic drug in the 30 days prior to study enrollment * blood donation within the past 6 weeks * participants who have engaged in a quit attempt in the past 3 months * specific exclusions for administration of guanfacine not already specified include: Hypotensive individuals with sitting blood pressure below 90/50 mmHG; EKG evidence at baseline screening of any clinically significant conduction abnormalities, including a Bazett's corrected QT interval (QTc) \>450 msec for men and QTc\>470 msec for women; known intolerance for guanfacine