Figure 3: Effects of chronic intravenous methadone (0.32 mg/kg/hr) administration on choice between cocaine and food in rhesus monkeys (). Abscissae: unit dose of cocaine in milligrams per kilogram per injection. Top ordinate: percent cocaine choice. Middle ordinate: rates of responding in responses per second. Bottom ordinate: number of choices completed. All points represent mean data SEM obtained during the last 3 days of methadone treatment. These published data  demonstrate that experimental manipulations can selectively decrease rates of responding and the number of choices completed without decreasing cocaine choice.