During the screening visit, you will be asked questions about your health, medication use, smoking history, and tobacco use. You will be asked about any current or past feelings of depression. Also, a small blood sample will be drawn (about 2 tablespoons) from your upper arm for a liver and kidney function test and a saliva sample will be collected to measure whether you are smoking. Women who are able to have children must have a negative urine pregnancy test. This session will last about 2.5 hours.