This study comprises two pilot experiments and a main study. Participants in the study will be screened with a psychiatric history, physical examination, electrocardiogram (EKG), and blood and urine tests. Participants will four testing sessions separated by 5 to 10 days. At each session, participants will be given one of two doses of alprazolam, diphenhydramine, or placebo (an inactive pill). Questionnaires and other tests will be performed.