Healthy young adults (N = 381 final sample; 200 male, 181 female) aged 18–35 years old were recruited and screened through a physical examination, electrocardiogram, modified Structured Clinical Interview for DSM-IV, psychiatric symptom checklist (SCL90) and self-reported health and drug use history. Exclusion criteria were: past year Axis I Disorder, history of mania or psychosis, less than a high-school education, smoking more than ten cigarettes per week, drinking more than three cups of coffee per day, lack of English fluency, or medical contraindication to amphetamine administration. Participants were inexperienced stimulant users: only 24% reported any previous use of stimulants and less than 2% reported 50 or more lifetime uses. Participants were asked to abstain from drugs and alcohol for 24 hours, nicotine for 12 hours and to fast for 12 hours prior to each session. At the start of each session, participants provided urine (ToxCup, Branan Medical Corporation, Irvine, CA, USA) and breath samples (Alcosensor III, Intoximeters Inc., St. Louis, MO, USA; piCO+ Smokerlyzer, Bedfont, Rochester, UK) to confirm drug, alcohol and nicotine abstinence, and female participants were tested for pregnancy.
