You have the right to leave the study at any time. If you choose to stop participating in this study, you will be asked to return to the clinic for a final clinic visit. At this visit, your complete medical history will be recorded, and you will have a physical exam and blood drawn for routine tests (about 3 teaspoons) and for research purposes (about 4 teaspoons). Your study doctor will also ask you about your current smoking use, any medications you are taking, and how you are feeling (symptoms).