General laboratory procedures
Each of these studies consisted of double-blind, randomized, within-subject, placebo-controlled sessions involving nontreatment-seeking individuals. Study duration consisted of three experimental laboratory sessions for the cocaine and methamphetamine groups (placebo and two active doses) and two experimental laboratory sessions for the alcohol group (placebo and one active dose) with no less than 24 h between sessions. Participants were phoned at least 24 h before each scheduled laboratory session and reminded to abstain from using any drugs including alcohol for the day before sessions but they should otherwise maintain their normal routine (e.g., sleep, caffeine consumption). Participants were also asked to refrain from eating or drinking overnight. Scheduled sessions began at 7:00 a.m. and were rescheduled if participants showed nonzero breath alcohol concentration (BrAC) levels. Participants who were regular tobacco smokers were allowed to smoke a cigarette at the start of each day’s session. Participants were then served a standardized low-fat breakfast (2 toast slices or 1 bagel; a single serving of jelly or butter; 355 ml of either apple or grape juice) which was finished by 8:00 a.m.