The four experimental sessions were conducted from 0900 to 1300 and were separated by at least 48 hr. Precapsule subjective reporting of mood was recorded at 0900. At 0930, participants ingested a capsule containing d-amphetamine (5, 10, or 20 mg) or placebo. For blinding purposes, they were informed that the capsule might contain a stimulant, sedative, or placebo. The stop task was administered by computer, 90 min after capsule administration, which is the expected time of peak d-amphetamine blood concentration. Mood measures were obtained 30, 60, 90, 150, and 180 min after ingestion of the capsule, and several other measures were obtained that are not reported here because of the specific nature of the hypothesis. These included the Digit Symbol Substitution Test (Wechsler, 1958), the Multidimensional Personality Questionnaire (Tellegen, 1982), Deviation From the Mode (de Wit, 2008), Addiction Research Center Inventory (Martin, Sloan, Sapira, & Jasinski, 1971) and the Drug Effects Questionnaire (Johanson & Uhlenhuth, 1980).
