in both monkeys , etorphine ( 0.0001 -- 0.0018 ) , meperidine ( 0.1 -- 1.0 mg/kg ) , morphine ( 0.1 -- 3.2 mg/kg ) , and codeine ( 0.3 -- 3.2 ) produced dose-related increases in the percentage of total session responses that occurred on the etorphine-appropriate lever .
C0026549
morphine
C0009214
codeine