Eligibility criteria were reviewed on the telephone with the subject. Those meeting all of the inclusion criteria were asked to make an appointment and were instructed to present to the Pediatric Clinical Research Center (PCRC) at approximately 8 am, where they remained for 24 hours. They were told that they may smoke their last cigarette prior to 8 am but must refrain from all additional smoking from that point on. Participants then underwent a brief physical exam, had exhaled carbon monoxide (CO) measured using the using the Vitalograph Breath CO monitor (Vitalograph, Inc.) and had blood collected for baseline cotinine and 3’-hydroxycotinine measurement. Blood was also collected at 24 hours post baseline for cotinine and 3’-hydroxycotinine measurement. Cotinine and 3’-hydroxycotinine were measured using liquid chromatography-tandem mass spectrometry (12). Next the participant completed a baseline questionnaire which included questions about demographics and smoking behavior. Participants were asked about the frequency and quantity of cigarette smoking, time since began smoking daily, and time since last cigarette smoked. The number of cigarettes smoked per day was calculated by averaging the number of cigarettes
