This study was approved by the Yale University School of Medicine Human Investigation Committee, the West Haven Veterans Administration Human Subjects Subcommittee, and the Radiation Safety Committee. The use of the radiotracer, [123I]5-IA, was approved by the Food and Drug Administration. Subjects were recruited by word of mouth, posters, and newspaper advertisements from the community. Eligibility was determined as follows. All subjects had a medical examination by a study physician to exclude any major medical issues or neurological disorders. This included a physical examination, electrocardiogram, serum chemistries, thyroid function studies, complete blood count, urinalysis, and urine toxicology screening. Subjects were given structured interviews using the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (SCID) to rule out any Axis I Disorder except for Nicotine Dependence. All tobacco smokers had to smoke ≥10 cigarettes per day for at least one year. Smoking status was confirmed by plasma cotinine levels >150 ng/mL, urine cotinine levels >100 ng/mL and carbon monoxide levels >11 on the day of intake. Smokers were helped to quit smoking using Clinical Practice Guidelines and contingency
